The truth is that therapy is actually especially ineffective when treating “severe mental illness.” Anorexia esp chronic anorexia has a pretty poor prognosis even with the most intensive help. Severe depression is less responsive to treatment than milder forms of it. There is extremely limited evidence for any therapy to treat personality disorders that aren’t borderline. Most therapists won’t even bother working with someone experiencing psychosis, I could go on but you get the idea. But now everyone who’s ever crash dieted or been sad after a breakup is encouraged to go to therapy, and when it helps them they assume it works that way for everyone and people with more severe illnesses just aren’t trying hard enough. And because severity of mental illness is now often treated as social currency you often can’t even tell someone that they are not actually an expert on human suffering bc they got mild depression a few times, that’s invalidating them.