Bad endings that ruin movies

So whats up with bad ending that ruin otherwise good movies? It's like, it's all good, but then it ends and the ending is stupid. Seriously? You know what? I'm not just going to rant on bad movie endings, but movies that start off good and turn bad. An example would be The Knowing with Nicolas Cage, it starts off really good and all like a good thriller, and then halfway through the movie it completely changes the mood into some weird sci-fi stuff. Whats up with that? The ending is stupid too. The kid goes to live with aliens or whatever? What? What is this? You have a perfectly good plot and movie in the first half. Then you have to turn around and start sucking? Why? The writers try to hard or overanylize or whatever and turn good ideas into bad projects. Why couldn't you just stick with the first half? Why'd you have to go all weird on me? Why? Because the writers lack so much confidence in there ability to write good stories that they throw them away for stupid sci fi and plots that make no sense. Or they have a stupid ending that makes you go "What the heck was that?". Like when movies build up and up and you think at the end something big is going to happen and it doesn't, and it's a let down and pretty much ruin the movie. Seriously. Well, I can't think much, so i'm gonna stop. Later