The tragedy is that you have to twist the knife in your own gray...

The tragedy is that you have to twist the knife in your own gray matter to make this defense work. You'll have to shut down, have to reject intellectual stimuli or diffuse them with sarcasm, have to cultivate stupidity, have to convert boredom from a malady into a way of confronting the world. Keep your vocabulary simple, act stoned when you're not or act more stoned than you are, flaunt ignorance, materialize your dreams. It is a powerful and effective defense - it neutralizes the insult and the frustration of being a vocational kid and, when perfected, it drives teachers up the wall, a delightful secondary effect. But like all strong magic, it exacts a price.

what does this quote mean? what tragedy is he talking about ? I cant understand it