One of our forefathers must have read a forbidden book.

If nature be regarded as the teacher and we poor human beings as her pupils, the human race presents a very curious picture. We all sit together at a lecture and possess the necessary principles for understanding it, yet we always pay more attention to the chatter of our fellow students than to the lecturer's discourse. Or, if our neighbor copies something down, we sneak it from him, stealing what he himself may have heard imperfectly, and add it to our own errors of spelling and opinion.

The greatest events occur without intention playing any part in them; chance makes good mistakes and undoes the most carefully planned undertaking. The world's greatest events are not produced, they happen.

To err is human also in so far as animals seldom or never err, or at least only the cleverest of them do so.

There are very many people who read simply to prevent themselves from thinking.

There are people who think that everything one does with a serious face is sensible.

I have often noticed that when people come to understand a mathematical proposition in some other way than that of the ordinary demonstration, they promptly say, "Oh, I see. That's how it must be." This is a sign that they explain it to themselves from within their own system.