Maybe you fear succeeding because you know that once you hit the top someone will be there to throw you out of your pedestal.
Your question led me into a spiral and I went to look for answers. That is when I found an article about self-sabotage. I have years of expertise in the field.
Aristoteles wrote "Nicomachean ethics" to his son and one of the points he made is that all human actions have happiness as an end goal. I agree with him and believe we fear not achieving happiness once we succeed. It's like realizing that your unhappiness was not related to what you thought was wrong condemning you to restart your search for the root or deal with the thought that you will be unhappy forever.
I will extend my rant a bit more and dare to add to my friend Aristotle's philosophy by saying; We look for happiness through love, but we fear giving love and being rejected. Once we refrain from loving we assume that others will do the same... it is a vicious circle of not loving once we fear not being loved
