When developers at Valve make a game, from the moment a single room has been crafted in their Hammer editor, they playtest it. Outsiders come in once a week, with no previous experience of the game, and play with whatever's been created. The developers must watch without comment, and observe how the player encounters the game.
This is not how Another World was developed. Released in 1991, Another World was the one-man project from Eric Chahi, a visually striking 2D platform game about a man transported to an alien world after a disaster with his particle acceleration experiment. (Which oddly enough is the very same premise as Outcast.)