At that recent organising course I got the tip of asking negative feedback of your students in order to improve yourself. I don't know why, but I just remembered it and did it 10 minutes ago.

Well, that took him quite by surprise and he could think of only one thing (which was perfectly valid). He'll think about it though next time we have a meeting, so I'm looking forward to getting some helpful feedback out of him!

It feels a bit strange to do this... It's the right thing, though.