My friend in Russia started to teach Computer Science (well, sort of) in two colleges. He wrote to me that he is probably a bad teacher (there was a more expressive epithet used, but I'll skip it :) because he concentrates all his efforts on those students who want to learn, and simply ignores the rest. I wasn't sure what to say, looked like a meaningful enough strategy... But today, reading memoirs of P. Kropotkin, a prince and a revolutionist, I found this: