Valve is known for its uncommon dedication to extensive playtesting -- Portal designer Kim Swift has said she was surprised at the rigor of that practice, which began in the very first week of Portal's production. During a recent Gamasutra interview, Valve's writer on Left 4 Dead Chet Faliszek addressed the reasoning behind extensive, early playtesting -- and stressed the importance of heeding the feedback that those sessions create. The Stages Of Playtesting Acceptance "When you first encounter using outside playtesters, you go through these stages," Faliszek explained. "They're stages of denial. The first time you go, you see the guy not looking at what you want him to look at, and he's not going to the right place. You're like, 'You're an idiot. We got idiots for playtesters. Who is this, somebody's friend? Let's get somebody who knows how to play games.'" "Then the second group comes through," he continued, "and you're still saying, 'Alright. Alright. You're stupid. What the hell? Who are these people?' Then by the third or fourth time, all of a sudden you're realizing, 'I'm an idiot. This is pretty obvious this doesn't work. It's not their fault, it's our fault.'" Inarguable Changes Faliszek drew a recent example from the development of Left 4 Dead by Valve South (known as Turtle Rock Studios before its acquisition by Valve), when Valve held a company-wide playtest around a particular multiplayer map. The writer called those internal playtests "brutal," because "everybody's name goes in the credits and we're all equal, and they want to make sure it's a good game." Just before the test began, a texture behind a ladder had been altered. "It was the minorest of changes!" he exclaimed. "Nobody saw the ladder. The entire playtest broke. Everybody got stuck on the third map, and complained about being lost. Once they got frustrated there, it all went to hell. It was so clearly, 'Yeah, that's not the right texture.' You cannot argue, or tell me that was the right texture choice." Making Painful Cuts Sometimes, playtesting demands changes that are much more significant, in terms of both lost development time as well as personal investment by the team. "With [Half-Life 2:] Episode One, we had this part where Alyx repaired power boxes, and you held a flashlight behind her," Faliszek recalled. "That's great -- cooperative play with a bot, you're helping her out. Boy, we didn't want to give that up. On paper, it looked like a home run. We were not going to give it up." In the end, the team had to give it up, creating new internal development terminology: "There was so much dialogue recorded and thrown away for Alyx using power boxes, so that any time something like that happens, it's like, 'Let's have a power box happen here.'" As Faliszek summed it up, "Playtesting is just proof to you. There's no way you can argue with that."