It's because we view our ideas as right, because they're ours. Since they're ours, if we say they're wrong we're admitting that we're fallible, something that humans don't particularly like doing. For the most part, people see themselves as the hero in a movie/game/story about their lives and we have been raised to see the hero be more or less perfect. Admitting error therefore means that we're not perfect, meaning either A) we're not the hero, or B) heroes aren't as perfect as we were taught, which would make us wrong again which goes back to believing we're above being wrong.
That's just my humble opinion, though. I could be wrong. I won't admit it, but it's possible.
Edit: Reread the question and realized that my answer doesn't address it properly. However, I'm lazy and it works well enough for me, so it stays. HA!