A lot of movies in the past has explored life as a series of pre-determined events and events that happen for a reason. This fatalistic outlook is very romantic in the sense that films tell us that no matter what the odds are, fate would find a way to put us in a better situation.
Knowing is a movie that looks into the possibility that life is already written and also looks at the other side-- where life is just a complete mess of randomness, a big glop of accidents and coincidences. Also throw a lot of apocalyptic and extra-terrestrials mumbo-jumbo, then you have a film that tries to say a lot of things. And that makes Knowing a big disappointment, despite Nicolas Cage's subtle performance.
Watching Knowing is like watching a patchwork of different genres-- thriller, action, and sci-fi, only that the pieces don't fit well. The films start of a mystery, where you wonder what the heck is going on with the predictions a girl made in the 1950's that all came true. Then it becomes an action-thriller where the disaster scenes are just riveting and, even disturbing. But when it devolves into a sci-fi "end of the world" epic-- all bets are off.
If I knew beforehand that Knowing would disappoint... well, you get the picture right?