A Story is told of a professor of a class in higher mathematics who asked that a complicated formula be worked out on the blackboard. The first student who came to the board began writing the solution to the problem, but after he had written the first step, the professor remarked to him: "No, that is wrong. Your procedure is incorrect." So the man sat down.
A second student was called to work out the formula, but the same thing happened to him; so he also sat down. Finally, a third member of the class was asked to work out the problem. The professor said exactly the same thing as before; but this man kept at his solution. The more the professor said No, the less the student heeded him. Finally he finished the problem.
The professor checked it carefully and declared it to be correct. The first two men were indignant. They claimed that their approach had also been right but that they had given up because the professor repeatedly said that they were not proceeding correctly.
