I have made plenty of mistakes.

I wraped around with a flogger.
I used a single tail wrong and left a long welt rather than the red spot from a single impact.
I used a cane wrong and broke the skin.
I used wax wrong and caused a minor burn.
I used a knife wrong and cut rather than scratched.

I absolutely learned from each of these, and in each case the sub didn't really notice until I talked about it with them.