There's an interesting expert discussion over on IGN that looks at the psychology behind the Pay-to-Loot systems found in many modern games. 

For context, "Pay-to-Loot" is the name given to the relatively new monetization system found in games like Overwatch, Battlefield 1, and Hearthstone that gives players the chance to earn randomized rewards by opening a mystery loot crate. 

In most instances, those crates can be earned or bought using in-game currency handed out as reward for impressive exploits and achievements. But as you'd expect, players can also spend real-world cash to speed up the process. 

What's interesting about the system is the way it lures players in by harnessing the power of chance. As noted by Jamie Madigan, a Ph.D psychologist who runs The Psychology of Video Games, there's a lot of research that showed fixed rewards -- i.e. cut and dried in-app purchases --  aren't as effective at changing player behavior as random rewards. 

"Our brains are wired to try to make sense of unexpected things. When you have a random number determining what loot you get, by definition, you’re going to get an unexpected result, or an unexpected predictable result every time," says Madigan.

"Whether you get that by playing the game for so many hours or winning so many matches, or whether you get a roll of that random number generator from spending five dollars to buy a pack of cards or a loot chest, it’s still the same rush, the same experience, the same hopeful anticipation to try and figure out, 'Well, did I figure it out this time?'

"Even though, in the front part of your brain -- in the rational slow-moving part of your brain -- you know that it’s completely random and, no, you haven’t cracked the code or figured it out. But those circuits are hardwired in our brain, and they’re very effective and very powerful."

To hear more experts weigh in on on the monetization model, by sure to read the full article on IGN.