Ignorance of all things is an evil neither terrible nor excessive, nor yet the greatest of all; but great cleverness and much learning, if they be accompanied by a bad training, are a much greater misfortune.
[Not enough is known about solid geometry] and for two reasons: in the first place, no government places value on it; this leads to a lack of energy in the pursuit of it, and it is difficult. In the second place, students cannot learn it unless they have a teacher. But then a teacher can hardly be found.
He who knows much about others may be learned, but he who understands himself is more intelligent. He who controls others may be powerful, but he who has mastered himself is mightier still.
I once heard a learned man say, "Every evil has its remedy, except folly. To reprimand an obstinate fool or to preach to a dolt is like writing upon the water. Christ healed the blind, the halt, the palsied, and the leprous. But the fool He could not cure."
Real wisdom is not the knowledge of everything, but the knowledge of which things in life are necessary, which are less necessary, and which are completely unnecessary to know.