A few months back, one of my first and best lab assistants, LZ, was graduating. We were at a ceremony/lunch for her and the other students who had received an undergraduate research fellowship.
I said to her, "now that you are graduating, I want honest feedback on how I can improve as a mentor, and what things I should think about changing." She copped out, going into a long list of all the things I do right, then asking me what things I thought I needed to work on. She's a clever one, if overly tactful.
I said, "that's a total cop-out answer." She persisted in answering without answering, and in pushing me to answer my own question, so I did.
I told her that there are two main things I feel I really needed to figure out better. First was the balance between autonomy (allowing students to do what they want in their own projects, even if it might not work) and direction (giving students a project that is very likely to work, even if it is not exactly what they want to do). Second, I thought I was pretty good at picking good students, and at mentoring good students, but not so good at knowing what to do about the disinterested students who I mistakenly hired and couldn't really motivate. I tend to assume everyone on my team is competent, interested and motivated, and when any of these assumptions is violated, it takes me a while to convince myself that there is little doubt to give the benefit of, and a longer while to figure out what to do about it. In typical LZ fashion, she consented without actually stating agreement.
Recently, I have been trying to tackle the second problem, approaching students who I didn't feel were getting it done and letting them know where I thought they needed to improve. The results so far have been quite positive, and I am hopeful that despite LZ's concerted effort to be unhelpful, my conversation with her has helped me improve my mentoring.