I've had many moments with counselors/psychologists where I felt that I knew more than they did about my mental health. It is ours and not theirs, we usually know ourselves better. The way I usually cope is by moving on, looking for whatever the person actually CAN do to help me, rather than what they can't do.
The worst occasion of incompetence in diagnosis was the counselor who told me after only a few sessions with her that I did not have any problems with self-esteem, because in her estimation, people with low self-esteem do not have a well-formed self-concept, and I do. Why is this terribly wrong? I have very low self-esteem, due to chronic depression and anxiety, and the only thing that has helped me had been working with people that improved my self-esteem through acceptance and love. Self-concept was a mute point, my having it makes no difference in how I feel about myself. I see myself as someone with many talents. I feel myself to be worthless and unwanted. Her assessment of me could have been very dangerous to my well-being. However, I kept her as a counselor to see what she could offer me in other ways. She helped me get forms signed to have a live-in-aide, and to be able to keep my cat when I moved to an apartment that would only allow pets that were needed for health reasons. When I moved, I found a better counselor. My new one has her moments of misunderstanding what would help me, but she is trying, and she has never sought to tell me I wasn't who I said I was.
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Let us comfort each other, and move tenderly when we are able. Let us hold hands and walk bravely, or fearfully together; for as long as there is Love, there is Hope, that everything will be okay, including the things we say are not.