Why would you leave a beautiful woman like that?

So I'm checking out the Yahoo page and there's a gorgeous blonde holding some award. She has a beautiful smile, blue eyes, and a cute button nose. I'm telling myself "OMG.. Reese is looking hot tonight".

Then I got to thinking why would a man cheat on that? I mean what was Ryan Philippe thinking when he cheated on Reese Witherspoon. Nobody cheats on her! She's beautiful on the inside as well as gorgeous.

It's happened to a few women who didn't deserve being left high and dry for someone else. Sara Evans, Jennifer Aniston, Shania Twain..etc Why would a man leave a woman like that? For another woman who isn't half as beautiful. It's like leaving a steak and lobster dinner for a Mcdonalds happy meal. It doesn't make any sense!