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.

The theoretical idea ... does not arise apart from and independent of experience; nor can it be derived from experience by a purely logical procedure. It is produced by a creative act. Once a theoretical idea has been acquired, one does well to hold fast to it until it leads to an untenable conclusion.

Everyday is an oportunity to make a new happy ending.

Whoever is careless with the truth in small matters cannot be trusted in important affairs.

When I was still a rather precocious young man, I already realized most vividly the futility of the hopes and aspirations that most men pursue throughout their lives.

I have made no secret, either privately or publicly, of any sense of outrage over officially enforced military and war service. I regard it as a duty of conscience to fight against such barbarous enslavement of the individual with every means available.

Common sense is nothing more than a deposit of prejudices laid down by the mind before you reach eighteen.