Featured Blog

Randomness in games... why?

Even though games tend to reproduce reality, and randomness is part of reality, why are game developers maintaining the factor chance in contemporary gaming? This rant is about asking for the reasons we keep randomness in games.

Angry bird

I am an angry bird. I am angry, because through playing this otherwise excellent game (Angry Birds, then) for the iPhone, I have come to hate the randomness found in the gameplay. What does that mean? It means that even if I am knowing the exact strategy for a level, and executing the manipulations seemingly perfectly, I still may fail the level. The success or failure of a level always seems to depend on someone throwing a dice and giving me a random result, disconnected from how well I achieved my strategy and moves.
The goal of the game is to kill static green pigs, protected by elaborate structures that can be destroyed or damaged using birds thrown by a sling. The player can control the way the birds are projected by the sling, choosing angle and strength, but once the bird is released, apart from an extra step which allows players to timely trigger special powers like explosion, acceleration, bomb dropping or others, there is nothing to be done anymore. The bird follows a parabolic trajectory, hits the structure or pigs and triggers a chain reaction of physical impulses that hopefully results in maximal destruction.

The point is that if you aim at a very precise point, anticipate the trajectory, see your bird hit the structure at seemingly exactly the same place as the previous attempt... the structure can collapse in a very different way than the way you expect it to collapse. As a result, you can as well reset the level before using the remaining birds, because you know that you can't succeed anymore at that stage. You are left with a feeling of waste, and have to try again and again with growing feelings of frustration, until when you hit the identified weak spot, it finally destroys or damages the structure the way you intended it, based on what you experienced before.

In a way it's a bit like Peggle: In Peggle, once you shoot your ball, the trajectory it will follow until it hits the bottom, and may hopefully be falling into the moving bucket, is unpredictable, and doesn't have anything to do with the player's skills. Once you've made your best move, randomness kicks in and you just can watch whether the dice will roll for you or against you.

This is the kind of situation that frustrates me to the core, and this frustration makes me want to rant. Actually, this article is meant to be something between a rant and a question: why do we put randomness in games? And why may it matter?

What kind of randomness are we talking about?

For starters, I think that randomness can be found in 2 different ways within video games:
- Randomness that happens when the game shuffles gameplay elements for a player to deal with. I would call it pre-randomness. That's the randomness that you find in card games, where the cards are shuffled before being dealt, or in Age of Kings, when you start with a randomly generated map.
- Randomness that happens in the expected results for a player's actions, delivering an outcome based on chance rather than skill. I would call it post-randomness. That is the randomness I described in Angry Birds, or in Peggle.

The difference between them is that in he first case, the player's reactivity or reflexes are put to test, and his skills can still be challenged, while in the second case, the player cannot react or have an impact on the game and the consequences of the draw.


Pre-randomness is very desirable for replayability, excitement and unpredictability of gameplay. It provides a shuffled set of conditions that good players, through assessment and analysis, are able to make the most of. When reiterated throughout the gameplay, it provides variety in challenges, i.e. one game is never the same as the previous. Using randomness in this context allows the player to prove that he is reactive and able to make fast choices to overcome a variation of a challenge he supposedly masters.

Examples of this pre-randomness could be found in Plants vs. Zombies: The spawning of zombies is randomized so that you need to adapt your defense depending on what kind of zombie spawned in which lane. In Tetris, each new piece is random and it’s up to the player to figure out where to place that new piece. In Left 4 Dead, you never know which special zombies you will encounter in the next room.

It’s interesting to note that this pre-randomness is usually followed with a delay before it impacts the player; the results of a random draw are announced to the player in advance, so that he can take enough time to assess the situation and react accordingly: In PvZ, once a zombie has spawned in a lane, it is usually walking slowly enough for the player to devise an appropriate reaction. In Tetris, the reflexion time is granted by the time the new random brick takes to fall down, and even the next random brick is shown to provide better forethought into the next move. In Left 4 Dead, the game provides carefully tailored random challenges: whenever a smoker is actually identified, and one player captured, the rest of the team has enough time to react to save their captured teammate.

So, while I am all for pre-randomness, what I rant about is post-randomness.


We are to expect from a video game to give the same outcome whenever we provide to it the same inputs. One typical example is combos in a fighting game: it is meant that each time we perform a quarter circle with the stick, quickly followed by the press of a button, our character will shout "Shyuriken" and throw a ball of pure energy. If this doesn't happen, we know that it is because we missed the correct timing or misjudged the needed amplitude, but we don't think that the move failed because of a rule that would state: "sometimes it does work, sometimes it does not work. It's random". The natural expectation of a player, when performing a move or giving an input to the game system, is to witness a result identical to the result obtained at the previous attempt using the same inputs. When reiterating a behavior, you expect to see the results match what you experienced before.

Examples of post-randomness can be found in Angry birds, as described above. One could argue that, due to numbers rounding  in the physics engine, even if one shot seemed to be exactly like the precedent, it could be off by a very thin margin, which will cause a different kind of collapse of the structure. That is true, but all in all, it’s all in the eyes of the player: He may consistently hit the structure at an identified weak point, but attempt after attempt, he has to rely on luck to succeed, instead of relying on skill. In Plants vs. Zombies also, there is chance involved with the corn catapult, for instance, that only has a percentage to send an improved projectile to stop enemies in their tracks.

If we leave behind physics engine approximations, that are more an undesirable effect of a necessary technology than an intended behavior, there are other examples of post-randomness:
Critical hits (among procs of all sorts) in RPG games like WoW and even in some shooters like Team Fortress 2, and spread zone for bullets in First Person Shooters like CounterStrike or Modern Warfare. There certainly are more, and I’ll be happy to read about the ones you like or dislike, but I’ll stick with these two.

Critical hits

Why have critical hits? Critical hits are hits that deal roughly double the damage as a normal hit. As such, they may, especially if they happen in a series, simply make or break a battle by doubling your DPS. Point is, the player does not decide when or how the critical hit will happen (save some exceptions like the rogue talent “cold blood” that ensures 100% critical hit, but it has a long cooldown). The game throws the dice at every hit, and there is only a chance each time to benefit from a critical hit. So, even though benefiting from a higher percentage of critical rating improves its probability, landing or receiving a critical hit is always the result of randomness.

Critical hits can be at most a good surprise in PvE gameplay, but where it really becomes a big problem is PvP: we've got here a game mechanic that can make a significant difference about who wins a duel, which is randomly triggered (and this applies for all the dodge, resist, and all the variety of procs that WoW provides). You end up in situations where one player feels frustrated and questions fairness because either his last hit missed, or his opponent crited twice in a row on him. The winner is then bragging on a victory that owed more to chance than his skills. Why allow this kind of situations happen, when it is perfectly possible to let skill alone decide about who is the best player? My opinion is that Blizzard is perfectly aware of this being a problem (as the game, in M. Pardo’s own words had initially and primarily been thought out for PvE), because the resilience stat has been introduced into the game right when PvP was becoming serious. Resilience’s objective is mostly to minimize, if not negate the critical hits uncertainty and unfairness, which goes to support my point.

A very recent game anouncement kind of supports this very point. Funcom have anounced Bloodline Champions, a game specifically tailored for competitive context. Presenting their game, I quote: “Completely Skill Based: Chance is not a factor. Spells and abilities do a set amount of damage and we've removed critical hits and passive avoidance abilites. Spells travel to your point of aim and can be avoided by enemy players, making every ability dependant on individual player skill!”. Now these are words sweet to my hears, and a game I definitely will want to play!

Spread zones

Why have spread zones? The spread zone is the area that is comprised within a crosshair, showing where bullets will hit when shot. Point is, your bullet can hit anywhere, randomly within that spread area. In many shooters, crouching or proning helps reducing or sometimes removing that area, but if you shoot your weapon while the area is relatively large, you expose yourself to hit or miss based on a pure chance factor. As long as the spread zone isn’t filled up with your target, you may miss your hit, not because you didn’t aim correctly, but because there was a chance that you would miss at a certain distance, regardless how well you were aiming.

Sure, the concept of spread zone means to replicate the very realistic fact that weapons are not 100% accurate. I agree, but only a few games (Flashpoint, Armed Assault...) actually try to favor pure realism over the fact that skill should override luck. Most FPS don’t stick to pure realism, so why try to be realistic through diminishing the impact of skill over luck?

Sure, the concept of spread zone is also meant to act as a counter to bunny hoping and ensure that players cannot headshot while running. I agree, but why choose randomization instead of increased challenge, like for instance increased bobbing while running, or faster crosshair movement? This would still make bunny hopping much more difficult, while removing the chance factor from the equation.

One additional problem with spread zones is that it may sometimes appear as a bug. How many times have we shot an unmissable shot, only to yell “WHAT? I had him RIGHT in my crosshair, how could I miss? This game is bugged”?

Most of the time though, thankfully, the spread area is small enough in highly competitive games so that its impact is barely noticeable, and the chance factor remains very minimal.

The essence of games: learning

All in all, post-randomness appears to be contradictory to the very essence of a game. Why is that? Because games are learning mechanisms: playing a game is based on re-performing actions that you've seen produce a specific result. You’ve learnt moves, and you reuse them to progress in the game. This is the fundamental principle of one cause gives one specific consequence. Once the player has verified that an action has a predictable outcome, he can perform that action at will, causing the consequences he is looking for. If one cause gives a random consequence, there is no learning possible.

Tutorials, which are easy games within the game, follow the same principle: “if you do this, this is what happens”. One at a time, the player is introduced to new game mechanics, new control schemes. He can then master the game mechanics and start solving the challenges provided by the designers, using the controls he has been given. The very essence of a game is to teach the player that when he performs an action, the result is always what he expects it to be. Once you introduce randomness in the results of a given input, you simply break that rule.

With machines that allow us to generate and apply precise algorithms, it is normally easy for any game developer to rule out randomness out of the gameplay. A computer program, given precise input (the press of a button, of a key, the movement of a mouse or of an analogic controller), should always give the same results after the algorithm of the gameplay is processed. Be able to provide a very deterministic experience is definitely within the realm of possibles.

If we take the most competitive games, the ones that really serve to measure skill of players and minimize the amount of luck involved, we find that Starcraft, CounterStrike, Quake, Streetfighter, don’t give much room to randomness, and that is why they are competitive.

Why may this matter at all?

Why is it interesting to know why randomness kicks in or not? Simply because from a legal point of view, some games could simply not be considered skill-based games while other can. What if a game is considered random enough so that the part of luck actually overrides the part of skill? A game like Monopoly for instance, while remaining interesting to challenge negotiation and diplomatic skills, could never be played competitively because of the luck factor introduced by throwing dice overrides most of the time the skills of the players. In Risk or Diplomacy too, battles can turn into an unexpected victory or a humiliating defeat on a dice throw.

How do you measure how acceptable it is to apply post-randomness in a competitive game, so that it doesn’t impact the balance and fairness of the encounters? And more than that, how do you make sure that a game can actually be presented as a game of skill instead of a game of chance from a legal standpoint? The question has some importance, as you have a very different legal frame if you wish to reward winners of tournaments with prizes.

Not being a specialist in legal matters, I will simply open the door for further exploration, but here are some interesting bits I found over the net:

In the Gambling Act 2005 from the UK government, a game of chance is defined as such:

In this Act “game of chance”—


(i)a game that involves both an element of chance and an element of skill,

(ii)a game that involves an element of chance that can be eliminated by superlative skill, and

(iii)a game that is presented as involving an element of chance, but

(b)does not include a sport.

This means that even if superlative skill may be used to win a game, as long as chance is involved at all, you may be classified as a game of chance.

And in this very instructive article about whether or not poker is a game of chance or skill, here are some interesting bits:

The decided cases hold that in order to be a “game of skill” the elements of skill must predominate over those of chance in determining the outcome.

That general rule is set forth in the California decision In re Allen as follows:

“The term ‘game of chance’ has an accepted meaning established by numerous adjudications. Although different language is used in some of the cases in defining the term, the definitions are substantially the same.  It is the character of the game rather than a particular player's skill or lack of it that determines whether the game is one of chance or skill. The test is not whether the game contains an element of chance or an element of skill but which of them is the dominating factor in determining the result of the game.”

“Even a contrivance that is predominantly a game of skill may be determined by chance.  For example, assume that a novice player of Bulldozer, through a minimal exercise of skill, has a 25 percent chance of winning an award.  Assume also that an experienced Bulldozer player, through the exercise of his superior skill, has a 75 percent chance of winning an award.  Chance would appear to predominate over skill in the former case, while in the latter case; skill would appear to predominate over chance.  Yet in either case, the outcome in each particular game played is ‘determined by chance.’  A player's level of skill may influence the degree of chance involved, but it does not eliminate the element of chance altogether. The outcome is always determined by chance because no player, through the exercise of skill alone, can control the outcome of any given trial.  It is chance that finally determines the outcome of each and every trial.  Thus, it is the incorporation of chance that is the essential element of a gambling device, not the incorporation of a particular proportion of chance and skill."


As a conclusion, I really advocate to have the factor chance (as in post-randomness) minimized if not removed from video games. Not only would it really better match to the essence of games as learning mechanisms, it would also reduce frustration of players by rewarding skill, and skill only. On top of that, it may even help to remove any doubt legislators could have about where to classify competitive games.

It’s only me though, and you may like randomness in games. Why would that be the case? I am looking forward to reading your arguments.

Latest Jobs

IO Interactive

Hybrid (Malmö, Sweden)
Gameplay Director (Project Fantasy)

Arizona State University

Los Angeles, CA, USA
Assistant Professor of XR Technologies

IO Interactive

Hybrid (Copenhagen, Denmark)
Animation Tech Programmer

Purdue University

West Lafayette, IN, USA
Assistant Professor in Game Design and Development
More Jobs   


Explore the
Advertise with
Follow us

Game Developer Job Board

Game Developer


Explore the

Game Developer Job Board

Browse open positions across the game industry or recruit new talent for your studio

Advertise with

Game Developer

Engage game professionals and drive sales using an array of Game Developer media solutions to meet your objectives.

Learn More
Follow us


Follow us @gamedevdotcom to stay up-to-date with the latest news & insider information about events & more