Honestly, I think teens should know that they are important. No matter how bad it is there's people that love you. If you did something a long time ago don't think about it, the other person most likely doesn't even remember it. Also do you remember when someone you barely know had a bad hair day? Neither does anyone when you do. Don't sweat the little things. Also be nice to as many people as you can as much as you can, you'll see how your life improves.