In my case it was a bad experience with a psychiatrist. But, I did not seek further therapy just to deal with that - I have other issues at the moment too.

I did find that when I mention the experience, most therapists jump not to "that was a dreadful experience" but to "why did you react so strongly? It must have brought up something from your past." As though being suddenly dumped by a psychiatrist you'd trusted because they insist you're suicidal (when you're not) isn't bad enough on its own?

Eta: oh, and as for trust, yes, it's hard, but it's like swimming - at some point one has to take off the water wings and just do it. If one wants to try therapy again that is - there are alternatives out there.