Sometimes we believe things because of the process of therapy. If a therapist says "try thinking of your inner life as a bunch of people who take on different roles, see if that helps your problem" (what Internal Family Systems (IFS) therapy is based on), and it does help, you probably won't be absolutely certain that you have a bunch of people who make you up as a community, but your credence in that will rise, and you may trust as though that belief were absolutely true.
Similarly (though this isn't exactly therapy), if a therapist like Freud says "your religious belief is created by a subconscious mechanism of wish fulfillment" and, when you hear of that, you think "it can't be true, can it? Can it? ... It must...", as though after thinking about it, you see that it is true, and then you lose your belief in God, obviously not founded on faculties aimed at truth-seeking, then that loss of belief can be taken to show that your religious belief was founded in wish fulfillment. (Was it really? Was it only founded in wish fulfillment? You did want it to be true as you would any good thing. Well, since you lost your belief, the therapy worked, so the ideas involved in the therapy must have been true, or "therapeutically true", as much as the notion that there are many people in you because IFS works.)
To be fair (to therapists), beliefs produced through the therapeutic process can be helpful (the goal of therapy), or even true, if the therapist is responsible to the truth.
We tend to believe whoever heals us, whoever changes us, or has decisive psychological power over us (often, whoever abuses us), whether or not they really know what they're talking about.