One of the most liberating and terrifying things you can do is to accept responsibility. For everything. Many of us grow up with the incredibly limiting belief that anything that doesn't go our way is someone else's fault. It's your teacher's fault, your friend's fault, your boss's fault, your partner's fault, the world's fault - whatever, as long as it's not your fault.
There is no surer way to hold yourself back than blaming your life and your setbacks on other people.
A particular pet peeve of mine is people who blame their character flaws on something out of their control. This takes a lot of different forms, such as, "I've got a bad temper, so he had it coming", or "Yeah, I'm just not good with responding to messages", or "I'm no good at talking to girls", or recently the popular anti-social excuse "I'm just not comfortable around people". Yes, I know that there are biological propensities for violence, anti-social behavior, and just about every other potential character flaw, but there's nothing worse than blaming malleable character traits on things out of your control. The mere belief that these things are unchangeable givens is at once a terrible excuse for our own behavior as well as a confining cage squeezing the life out of our future selfs.
The sheer magnitude of important stuff not taught in school is fairly overwhelming, but how to deal with other people, and how to deal with our own thoughts, emotions, and especially shortcomings - in other words, skills related to emotional intelligence - are perhaps the most glaring omission. It turns out that these are skills that can be learned, and the value is arguably greater than anything else you may learn in life. How do I know that we can change the way we deal with other people? Because I've seen it in others, and I've seen it in myself.
No one can force you to change. No one can force you to become a better person. It has to start from you - there is no other way. It starts from simply accepting responsibility for everything in your life. Once you accept personal responsibility, your life is something in your control. It's hard, it's painful, and sometimes it really, really sucks, but it's also the healthiest thing you can do if you're looking to grow as a person.
From now on, rather than looking outward and directing your blame at others, look inward. You'll be amazed at how freeing it is.