I have to say, the biggest problems I see are: fear of rejection and belief in social conditioning. Sorry to break it to you, guys, but fear is never a good excuse not to do anything. Fear can be overcome. It doesn't matter if its fear of spiders, fear of heights, or fear of failure/rejection. All fears can be overcome or controlled. The best way is exposure therapy. Expose yourself to whatever it is you are afraid of, but repeatedly and in controlled circumstances. If you are shy, start out talking to random people, and gradually work it up to actually asking people out. If you are a afraid of failure/rejection, then practice the great art of failing/getting rejected, so that you become desensitized to it. In everyday life, just say things that you know people are going to disagree to, then work it up to asking people out when you know they are going to say no. I use to be both really shy, and terrified of rejection, but now I am not. Anytime my fear of something stands in my way, I use a greater fear, my own fear of death. When you truly remember the fact that you will only live once, and that life is not infinite, can you truly say this measly fear of rejection is strong enough to stop you from moving forward?
The other crappy excuse is things born from social conditioning: "I am ugly", "I am poor", "I am stupid". None of these things truly matter to most people, and the few that that they do matter to, are not worth your time. We believe these things, because of the media, despite the fact that they are honestly not true to real life. No one is perfect, and no one needs to be. With over a trillion people in the world, can you honestly say that everyone is going to dislike you?