The one thing that really frustrated me: a client had a program to do on her own at the gym. She saw somebody doing ‘something’, tried it herself and got hurt as a result. If she had described the exercise to me, I could have dissuaded her from trying (hopefully), because I could have anticipated the resulting problem.
This happened a few times; we parted company amicably. I had to console myself that I had done the best I could.