Some theories are good for nothing except to be argued about.

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.

If people should ever start to do only what is necessary millions would die of hunger.

Why does a suppurating lung give so little warning and a sore on the finger so much?

He swallowed a lot of wisdom, but all of it seems to have gone down the wrong way.

To do just the opposite is also a form of imitation.

Everyone is perfectly willing to learn from unpleasant experience - if only the damage of the first lesson could be repaired.