Clients become quite fearful of admitting that they weren't successful since the last time they had a session. This could include not succeeding in using a coping skill that they're learning about, or not being able to complete a homework assignment I gave them. Humans aren't robots, and therapy is a lot of work.
That being said, I don't expect people to be perfect as they start to work on themselves in a positive way. It takes time to really commit to change, especially in relation to trauma or conflicted views that an individual holds. I feel as if the client doesn't want to let me down as their therapist, but these "failure" events are just as important to talk about as successful moments!