I've been told on multiple occasions that I apologize too much. It's not that even something I consciously do. Sometimes, I just feel really bad that I wasn't able to make things work out for someone the way I thought it should have, or I feel like I've inconvenienced them in some way. Sometimes it's true. Other times, no one really cares.
If they were inconvenienced and don't have a heart of stone, even the gruffest library patrons are usually mollified by a steady stream of timid sorry's.
Sometimes, though, they feel the need to point this out to me. "You know," they say, "you don't have to keep apologizing!" Or, the more embarrassing "You say sorry a lot." And what's the proper response? Probably "Oh, I didn't realize," or maybe I should just laugh it off.
But, instead, I just say "I'm sorry".