I think this is one of the most primal of all fears. If we posit that the two most basic existential questions are “why do anything at all–why suffer when we have an alternative”, and “what should be done”, then allowing the possibility of qualitative alteration to enter your consciousness is tantamount to an attack on your identity.
This is the root of dogmatism. Fear leads to the building of thick, high walls, moats, and defensive artillery. If you are afraid of the dark, if you are afraid of existing in a condition of the periodic confusion that necessarily attends perceptual growth, then you will stagnate, and never know it.
The point here is that you can go very fast and very far, on rails. Trains are efficient, since they can only go along very clearly specified paths. Fanatics are often good workers, since they don’t have to question–even for a moment–what they are doing. Yet anyone who doesn’t periodically ask big questions all their lives has stunted their growth thereby.
You have to be open to big changes, and that takes courage. Very few people possess this courage.