Why is it so hard for a guy to admit that he messed up and apologize?

I've since had more experiences with women who absolutely will not admit they've done anything wrong, even after they've done something terrible, and some men (well, one anyway) who will apologize when he knows that he messed up. So I probably should have worded this question "Why is so hard for some people to admit that they messed up and apologize?"

I still don't understand this about some people. One thing that baffles me is that some people will apologize profusely for little things, but never apologize at all for big things. What's up with that?