I used to say "sorry" all the time. For everything: my existence, being seen, speaking, etc.

I have always used the word "sorry?" as in "pardon me...I did not hear you."

Lately, I have been working on saying "sorry!" when I make a social error or something (such as talking over someone, accidentally bumping into someone or inadvertantly turning off the lights when there is someone still in the room). Or for instance on PC when I truly understand someone's pain and want to be supportive.

I reserve "I apologize" for those times I feel I have had a lapse in judgment, made a sincere mistake or if someone calls me out on something and feelings are hurt or there is tension.