Working out and age.
It really is true that you give less fukks as you get older, and realize you were stressing out over way too much in your past.
Nobody is perfect, everyone has their insecurities, we're all making this life thing up as we go along, and everyone has the persona that they want you to see.
The more I reflect on that, the easier it is to accept failure, rejection, embarrassment, etc.. If someone made you feel less confident, they will forget all about it in minutes. You have to learn to let that chit go. We're all going to be fukking dead one day. DEAD. UNALIVE. EVERYBODY. So fukk wasting time not feeling good about yourself, no matter where you are in life.
Yeah, work to improve. Always try to do better, but you're player one in your life. You matter more than everyone (barring the family you make of course). Enjoy your life. Laugh at yourself and the absurdity of existence, relax, and enjoy this short ride.