Fear of Success
Though you might be unhappy in your current situation, you might find a sense of comfort there. Because once you succeed you’re being thrust into new territory, have new responsibilities, and you have to be more accountable. So you stay in your current situation because it’s what you’re sure of.
Instead of seeing success as a means of new pressure, see it as proof that you were up to the challenge. Prove to yourself that if you succeeded before, you can certainly do it again.