I suppose that as far as your second question, "where does the frustration come from," it's about both needs and expectations, the fact that clients and therapists can often have different visions of needs and expectations and how to meet them, the fact that frustration is an inevitable part of life, and the fact that sometimes some therapists don't handle their clients' needs/expectations skillfully or professionally.

Personally, I need my therapist to be smart, compassionate, reliable, and attentive in our sessions. I need him to be unbiased and at least somewhat knowledgeable about the communities I'm a part of. I need him to take responsibility for "meeting me where I am," and for guiding the interaction in a therapeutic direction. I need him to be precise about understanding what I'm saying, and open to being corrected about misunderstandings.

And it's taken a lot of trust-building for me to transform those needs even partially into real, internally felt (albeit still fragile) expectations, because of the number of abysmal past interactions I've had with therapists who treated one or more of those needs as expendable or excessive. Many of us come to expect the same bad interactions we've had in the past, which can make it complicated to reshape things to have better interactions and relationships (which, isn't that the whole project of therapy for so many people?), and therapy relationships are no different in that regard.

In the past, I've continued to see bad therapists because I doubted my own perceptions of the ways they were failing to meet my needs, whether because those failures were somewhat subtle, or because I was blaming myself for "needing too much" when they demonstrated that they didn't or couldn't meet those needs. There's a power imbalance built into therapy that can make it very, very hard sometimes to accurately assess the situation.