My umpire side of me will say this (even if for me it's tennis). All umpire are human and we do make some mistakes. I know that, personally when I make a bad call, I realize it and I feel bad for a while after it, you just gotta try and forget about past call and concentrate on the next one, they say.
I have to say that about the course of remedial, like instant replay, it is a good thing, but, at least in tennis, you'll realize that most of the time we make the right call, if not, the chair umpire will get it right. Now for other sports, well I know that for football, (at least in the CFL) most of the original call does stands.
But I gotta admit that in spite of all that, bad call still exist and sometimes it influence the game. Nothing can be perfect