Because you apparently have to hit the little white ball into another ball. One would think that wasn't a terribly difficult thing to do. However, I managed, several times, to hit absolutely nothing with said little white ball. And I was trying to hit a colored ball. And the one time I managed to hit a ball into the pocket, it was the 8-ball, and I wasn't aiming for it. And apparently you loose the game immediately when you do that. Doh!
But I did have fun hanging with some work friends after work, so despite the horrid attempt at playing pool, I had a good time.