No paradox, no progress.

You can recognize a small truth because its opposite is a falsehood. The opposite of a great truth is another truth.

Every great and deep difficulty bears in itself its own solution. It forces us to change our thinking in order to find it.

Anybody who is not shocked by this subject has failed to understand it. [of quantum mechanics]

A physicist visits a colleague and notices a horseshoe hanging on the wall above the entrance. 'Do you really believe that a horseshoe brings luck?' he asks. 'No,' replies the colleague, 'but I've been told that it works even if you don't believe in it.'

There are trivial truths and the great truths. The opposite of a trivial truth is plainly false. The opposite of a great truth is also true.

If an idea does not appear bizarre, there is no hope for it.