So a brief bit of my own experience first.

I think a lot of my problem in therapy was that the therapists were trying to break through defense mechanisms and get me to challenge unhelpful thought patterns and all that. Only, in retrospect, the therapists were exactly wrong. We're talking things like trying to challenge unhelpful behavior patterns that were keeping me from getting support from my family, when the truth was that my family was abusive and the things the therapists were trying to get me to challenge were the ones that were keeping me safe. Or with the recent ADHD diagnosis, therapists were constantly trying to get me to challenge the supposedly distorted and unhelpful idea that I might actually have something different about how my brain works. Turns out that was exactly the truth.

But then I'd talk about this and people will say things like, therapy is hard and you have to be open to new ways of thinking. Or that a therapist who just agrees with you all the time isn't helpful. And you shouldn't quit therapy just because you're uncomfortable or don't like what the therapist is saying, because if you do that you'll never be able to get better.

The trouble is these two events in therapy look exactly the same from the client perspective, so far as I can tell. And most stuff on keeping yourself safe in therapy seems to start from the assumption that you're already in a basically safe place and able to confidently tell the difference. When the fact that we don't understand or aren't sure is often what drives us to seek therapy in the first place.