A complete loss of trust or fear of such complete loss of trust is where I would leave. After enough negative, unfixable emotions would accumulate in the therapy relationship. Mainly due to the therapist's detachment, lack of empathy, manufactured attitudes, lack of transparency, and sometimes actual passive-aggressive manipulation, e.g. by deliberately not responding to me when responding to other clients' messages (but pushing it in my face that they are responding to others anyway!!), or by claiming mysterious insight when expressing bad attitudes and opinions towards me. All that in the face of me trying to trust them enough, no way I'd continue therapy with a therapist like that.

I would say I gave such people a chance if it was some negative reaction in me that I would dismiss instead of analysing it out enough to discover the therapist is doing something that's just completely not okay, because of me trying to trust would make it hard to want to see negatives like that. If the accumulated negatives became too much, then the last straw would push me over the edge. At that point there was no way for me to turn back. As I would start analysing all of it consciously and arrive to a decision to stop therapy.

I would consciously decide to leave if I saw that that would make me more stable than staying with the therapist. That's how I've done it before. I did learn deep therapy is not for me, if I'm supposed to have attachment to the therapist and they do not have one to me, then it's not a real relationship to me where I can work on anything. The balance of power is simply too unequal without external checks for it. E.g. supervision, evaluation of objective feedback, etc.

EDIT: if it counts as giving a chance, after making that decision, I'd still ask them about the main issues in the last session. But they were like, justifications, rationalisations, no real interest in trying to work with me. So I did swiftly end the therapy at that point.