When you watch a film, you just want to watch something and be passive. When you play a game you want to be the actor, you want to be in the shoes of the guy making the decisions so it's a very different type of experience.
You always need to reassess what you know, or what you think you know, because the technology and the concepts are always changing.
You also need to imagine what is going to work tomorrow, not just what worked yesterday. You have to be enthusiastic and you have to have passion.