I can only give an example from my own experience. I have come to a point in therapy where I can say, this is a core belief of mine (an unhealthy one), whereas before I could not even name it without shuddering and tears

so now after all this time, I can say it.... and now T wants to talk about where it comes from, and I find huge resentment building over being asked to talk about all that. This is fear; the subject is not safe.