How Do I Know What I Think Until I See What I Say?

Sometimes, during the course of reading something or watching something, I'll get annoyed by something a character does and put the book down or turn off the television show. Permanently. when that happens, I'm usually thinking "whatever. Character X would never do that!" Let me give you an example--a long, long time ago, in a land far far away, I used to watch a show called Joan of Arcadia. If you didn't see it, the plot's not really important,* but what is important is that there was a guy who liked her named Adam. Adam was a really sweet kid, an artist, kind of spacey and dreamy, so much so that he called Joan "Jane" for most of the show, but a basically awesome kid. And eventually over the course of the show's two seasons, Adam and Joan end up being a couple. Then, at some point in the show's second season, Adam cheats on Joan. And not just "I kissed this girl and it will never happen again," but totally "I used thi