You can never solve a problem on the level on which it was created.

You imagine that I look back on my life's work with calm satisfaction. But from nearby it looks quite different. There is not a single concept of which I am convinced that it will stand firm, and I feel uncertain whether I am in general on the right track.

Even if you have to go through hell - go without hesitation.

One should never impose one's views on a problem; one should rather study it, and in time a solution will reveal itself.

The most evident difference springs from the important part which is played in man by a relatively strong power of imagination and by the capacity to think, aided as it is by language and other symbolically devices.

What physics looks for: The simplest possible system of thought which will bind together the observed facts.

You can never solve a problem on the level on which it was created. Insanity: doing the same thing over and over again and expecting different results. A life lived for others is a life worthwhile.