The sensitivity to rejection is psychological and this is actually over sensitivity to the rejection procedure from anyone and this happens to people who are in a neurotic state of mind. The borderline cases of neurotic disorder are all about the suffering of the person who are working themselves tired of their own fear of rejection. There are many ways to get out of such fear and you must find the right kind of methods so that you can sync yourself with such behavior and keep your fear behind. The psychologists try to get you over this with various talk therapy but if you know that you have such a condition then you are the best person to guide you.
Ask for what you need without others handing it to you. There are a few things that you should follow so that you will come out of such fear that is abnormal. This feeling is full of pity for oneself and the intention to please others to get the rejection at bay. Your fear of rejection stems from not asking something that you should have or you can ask but the fear stops you from asking. Then you see the other people going after what they want and they get the things that they need but you keep on waiting till life hands you something that is left over from the others.
Never stop living and trying but not by punishing yourself.
There are different things that you have let go because you had no intention to ask for that thing. You should also learn to take rejection with ease. You will find rejection is part of life and if one rejects your book you must try the next publisher but never give up trying. The next thing is that you must not punish yourself but strive for a better life. You have a right to enjoy the life.
You must learn to stay in the present moment and do not go back to the past and keep losing yourself in the mistakes that you think you have made. If they are mistakes then they have given you some knowledge and you are wiser now for them. The fear of rejection also should not allow you to nurture hatred for someone in your mind. Forgive others so that you do not carry the burden of hatred around. This makes you worry more about pleasing a single person and start taking your opportunity to grow with a smile on your face and a positive thought in your mind.