Self defense, man. You are trying to defend yourself from failure, but you don't need to do that.
So there is this indoor swimming pool in my hometown and it has a tower which you can jump off from three different heights (1m, 3m, 5m). Young me wanted to be as cool as all my friends who already jumped off the 5m spot. As I slowly walked towards the edge I felt my knees shaking in fear. Watching someone jump off it looks so easy, but standing there yourself is a completely different story. My toes touched the edge. I looked down and almost fainted because it looked scary as fuck, like ten times higher. What if I fell in a dumb way and hurt myself? What if the others laughed at me? What if I chicken out and climb back down, will I be a loser forever? My friends became impatient already and asked me to jump the fuck down now. In the end it took me several minutes to jump and I was really scared, but I did it anyway.
What I'm trying to tell is that sometimes you just need to act, even if you're afraid of the consequences. Because only then you will know what you like and what not, and only then you can expand your limits. After I jumped off that damn tower it suddenly lost every bit of scare, and so do many other things in life as well once you tackle them. I know this is not applicable on everything and anything, but on many things. This is in some way similar to what Darthmetallicube tried to express, I think. Just do something and learn from it. And also learn from failure. Everybody - boys and girls alike - is scared as fuck to approach somebody for the first time and just have a normal conversation that may or may not end in a relationship, but they say practice makes perfect for a reason. The more you do something the better you get. And yes, I believe that this is applicable to social skills as well. The more you deal with people the better you understand to behave among them. Nobody gets born as a social idiot. Everybody has the option to improve.
Pessimistic people often share a great fear of failure. It is okay to be a pessimist. I don't think pessimists are instantly bad and optimists are instantly good, but I think that pessimists tend to limit themselves much more than necessary. I see that in your posts as well, but I really don't think you need to do that. You're cool. Stop making excuses and gain some experience, no matter which kind.
Life is an RPG after all.