@Something Funny From my personal experience of observing people and overcoming this problem myself, I'd recommend exploring your shadow deeply and then integrating it in your conscious life. Sounds simple, but it is among the bravest things you can do. After facing your internal demons, nothing external will phase you, because ultimately it's all just you. It seems you are simply afraid of yourself. And I mean that literally.  
Jordan peterson has a good take on this. He phrases it as "Become a monster, and then learn how to control it". The idea is that once you explore all the terrible aspects of yourself that you have been hiding because they don't fit your self-image, you develop self-respect. And once you have self-respect, you will become more decisive, assertive, and courageous. 
It's like having a loaded gun. When holding it comfortably, like you own it, you feel the power, confidence, and a sense of invincibility. But if you have never held a loaded gun, you might be scared to pick it up at first. Loading the gun is like becoming a monster, and then making it your own is like learning how to control the monster, which also involves developing a degree of respect for it because it can potentially kill others and yourself.
The same is true for the shadow, there is potential in there to kill others and yourself. 
While exploring the shadow, remember the wise words of Carl Jung:
"That which we need the most will be found where we least want to look.” 
and 
"No tree can grow to Heaven unless it's roots reach down to Hell."