An expert is a person who has made all the mistakes that can be made in a very narrow field. - Niels Bohr

If a scientist does not understand a problem, he writes down many formulae, but as soon as he has understood it, there remain at most two.

Two sorts of truth: profound truths recognized by the fact that the opposite is also a profound truth, in contrast to trivialities where opposites are obviously absurd.

You must come to Copenhagen to work with us. We like people who can actually perform thought experiments!