The religions of mankind must be classed among the mass-delusions of this kind. No one, needless to say, who shares a delusion ever recognizes it as such.

I am actually not at all a man of science, not an observer, not an experimenter, not a thinker. I am by temperament nothing but a conquistador

The facts which have caused us to believe in the dominance of the pleasure principle in mental life also find expression in the hypothesis that the mental apparatus endeavours to keep the quantity of excitation present in it as low as possible or at least to keep it constant.

But the less a man knows about the past and the present the more insecure must prove to be his judgment of the future.

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.

The genitals themselves have not undergone the development of the rest of the human form in the direction of beauty.

Opposition is not necessarily enmity; it is merely misused and made an occasion for enmity.