Difficulty. It is something that no entertainment medium other than video games has to contend with. Our input as players defines our experiences with our games, in particular how challenging they are. One need only be present for a song or movie to finish in order to get the full experience. In order to get through a game however, one must be skilled enough to adapt to the requirements of whatever game is being played to "win" in the end. Some games give us fairer challenges than others, and it is in evolving game design where either frustration or satisfaction on behalf of the player are born.
So gamers, make the jump if you want to know what makes us tick when it comes to facing our virtual demons!