Burning Bridges

Why is it that in a connection based industry people burn their bridges? I quite understand not liking someone because of their personality and getting frustrated with people who don't have common sense, but really, does it have to come down to constantly being mean to them just for being in your group? You have no idea what's going to happen in the future and for all you know, the person who you loathe makes it big and offers jobs to people that you may end up needing.

I'm in two industries that are based on connections and from what I know of, I haven't burned a single bridge. Yes, I may not like the person and I may constantly rant about them, and vice versa, but when it comes down to it, I will bite my tongue and work with them because that's what you're gonna have to do. Why is that concept so hard to grasp?