As long as they have been through their own therapy (which is a requirement to be allowed to practice in many places, and ought to be a requirement everywhere, in my opinion) I think they understand. Nobody can ever know exactly what kind of impact or influence we have on anyone else, but I think anybody who has gone through adequate training to become a T, and who has sat in the clients' chair themselves for hundreds of hours, will understand the potential impact they may have, even if they can't know exactly how it feels.