Every barrier is psychological, and those are the hardest ones to break down. There aren't many people anymore who can take the pressure of their peers and culture in stride. So, for the average person (and especially for the above-average person), walls are built up in the psyche that disconnect them from their potential. They stop listening to themselves, and start listening more to the television, and so they never realize anything they could accomplish. If they can even accomplish anything at all.
Strangely enough, the easiest way to break psychological barriers is to break physical ones. Start training for a 5k or lifting more weight than you ever have before. If you're the kind of person that could set goals for yourself in the first place, you're the kind of person that can achieve them. And then you'll find it's harder to be lazy like you were before. And soon you'll find out that it's not that hard to talk to that girl who lives in the apartment across the hall, or tell your boss to suck a dick, or to leave your current life behind and start in a new place, maybe far away from where you are now.
It sounds simple enough, but people tend to make it harder than it is. Self-helpers and new age morons spend a lot of time and money reading and writing books about this, and then continue to sit on the couch when they're finished, thinking that the "positive energy" they give off will bring them everything they want. The few who carry out their plans don't have time for that.
Or, alternatively, you could let the pressure build and then go jihad and kill lots of people. That's becoming a little cliché, though.