Indeed, the great Leonardo (da Vinci) remained like a child for the whole of his life in more than one way. It is said that all great men are bound to retain some infantile part. Even as an adult he continued to play, and this was another reason why he often appeared uncanny and incomprehensible to his contemporaries.

I consider it a good rule for letter-writing to leave unmentioned what the recipient already knows, and instead tell him something new.

In general people experience their present naively, as it were, without being able to form an estimate of its contents; they have first to put themselves at a distance from it - the present, that is to say, must have become the past - before it can yield points of vantage from which to judge the future.

The dream is the liberation of the spirit from the pressure of external nature, a detachment of the soul from the fetters of matter.

The true believer is in a high degree protected against the danger of certain neurotic afflictions; by accepting the universal neurosis he is spared the task of forming a personal neurosis.

Even if all parts of a problem seem to fit together like the pieces of a jigsaw puzzle, one has to remember that the probable need not necessarily be the truth and the truth not always probable.

The most complicated achievements of thought are possible without the assistance of consciousness.