It is shocking that young people should be addling their brains over mere logical subtleties in Euclid's Elements, trying to understand the proof of one obvious fact in terms of something equally .. obvious.

Euclid for children is barbarous.

Theory is the essence of facts. Without theory scientific knowledge would be only worthy of the madhouse.

The best result of mathematics is to be able to do without it.

Why should I refuse a good dinner simply because I don't understand the digestive processes involved?

Shall I refuse my dinner because I do not fully understand the process of digestion?

...there is no absolute scale of size in nature, and the small may be as important, or more so than the great.