We all regret something in life

What do you regret? I could think of alot of things I regret. The very first of them would be when I chopped off all of my baby hair at age 3. My hair grew out rather funny after that, it was never the same... looking at my sister I always imagine thats how my hair would have turned out and I get jealous. Lastnight one of my sensei's told me and my friends that he regretted only one thing in his life/marriage, that he never had kids (he's 80). Unfortunately we cannot take ANY of it back. And really, sometimes I feel that it'd be better if we don't change things, because we wouldn't be the same person. It's funny how I can have all these Zen moments, I can know what should or shouldn't be done/said, and yet I am still human enough to do the wrong thing. At least I know what I did wrong I suppose. I don't know how many other people ever admit to doing something wrong.