Man is, at one and the same time, a solitary being and a social being.

Failing isn't bad when you learn what not to do.

There are six-million shots in the game of pool.

Most people see what is, and never see what can be.

A conviction akin to religious feeling of the rationality or intelligibility of the world lies behind all scientific work of a high order.

Physical concepts are free creations of the human mind, and are not, however it may seem, uniquely determined by the external world.

We come now to the question: what is a priori certain or necessary, respectively in geometry (doctrine of space) or its foundations? Formerly we thought everything; nowadays we think nothing. Already the distance-concept is logically arbitrary; there need be no things that correspond to it, even approximately.