It's a recipe for disaster because the client has weak defenses and the therapist doesn't have to be vulnerable themselves. The therapist occupies a position of authority also.
The Regina Hurt person I told you about before would be like 'I am shy about singing in front of a stage. See, everybody has problems. Now then, tell me about the time you were sadistically sexually abused so I can use that against on you and get off on it while pretending to society that I'm a good person.' Like as if experiencing a little stage fright was at the same level of the heavy serious crap she wanted you to reveal. And sadly, her manipulations often worked, because she actually does have a very good external reputation in the superficial by-the-book sense. But yeah it was pretty repulsive. She also would try to anger and emotionally abuse/belittle you enough in hopes that you would assault her so she could then press charges. This one didn't work as much, but it didn't stop her from trying.

"I really care about you, you can tell me." (minor tells her personal things) "Okay now I am going to try to escalate you to a higher security prison."

Also @Aramas what you said about identicals being sadistic, I feel that. I think especially male and female IEIs can sort of be sadistic with each other, and it can be dangerously subtle and kind of like socially trying to sabotage each other while having the facade of innocence. Female IEIs have drained my mental health too much where I stay away from them lol. Maybe you could sort of say 'it doesn't work because it's two like charges and putting batteries in a game boy backwards' but it's not quite that simple.