Good therapists have worked intensively with themselves and their own trigger points. Otherwise the client will always reflect their own vulnerabilities back to them, making it difficult to maintain a neutral position. Only when they have worked on these sore spots can a therapist be truly present and listen non-judgementally.
It is also essential for the therapist not to identify with the success of the sessions. Sometimes the client is simply not open for them yet and has to find out more things for themself. If a belief that, “I am not good enough” starts to form in their subconscious, the therapist may suffer from self-doubt, and the subconscious pressure to succeed makes subsequent sessions uncomfortable.