The biggest problem with teaching is that its results are dependent on the student, who only really learns what he wants to learn. It is curious because, if the student is genuinely interested, he does not need a teacher. And then we can imagine how much less difficult the path of learning would be for him, how useful it would be to provide him with shortcuts beforehand, point out the solution to expected obstacles and offer him an itinerary that only prolonged study is capable of outlining. All this is true, but it is true as long as we consider the ideal student. Serious study is never imposed on the average student. And the ideal student, who only comes across the teacher by chance, will perhaps also by chance be compelled to take the difficult path that only he will follow.