He prefers to face a blackboard and to turn his back on the class. He writes a , he says b , he means c , but it should be d . Some of his sayings are handed down from generation to generation. In order to solve this differential equation you look at it till a solution occurs to you. This principle is so perfectly general that no particular application of it is possible.
Geometry is the science of correct reasoning on incorrect figures.
My method to overcome a difficulty is to go round it. A method is a device which you used twice. Even fairly good students, when they have obtained the solution of the problem and written down neatly the argument, shut their books and look for something else. Doing so, they miss an important and instructive phase of the work. A good teacher should understand and impress on his students the view that no problem whatever is completely exhausted.