Stop focusing on the past on all the things you could have done, on all the things you should have done; don't beat yourself up for the things that you did, or the things that you didn't do, or the things that went wrong along the way.
You get so caught up in the past, in the missed opportunities, in the last potential, that you allow the things that are sitting right in front of you to pass you by. It is so much easier to look back and play out all the reasons why it didn't work than it is to look forward and decide that you are not going to take it anymore. It feels safer to be a victim of your shortcomings or circumstances of those who weren't there for you than it is to try it again, or try something new and risk failing.
It's so much more comfortable to live a small, safe life where you're able to get by (you're settling for okay) than it is to work your butt off to be extraordinary, especially when you feel yourself slipping into the past and playing out how it should have been, how it could have been, how things should have gone.
Slap yourself. Because you have today, you have tomorrow and you have the chance to sit down and ask yourself what's next. And then you just need to go out there and make it happen. You cannot allow your friends and family to keep you from achieving your goals.