An animal so poor in spirit that he won't even fight on his own behalf is already an evolutionary dead end; the best he can do for his breed is to crawl off and die, and not pass on his defective genes.

- I'm so busy doing what I must do that I don't have time for what I ought to do... and I never get a chance to do what I want to do! - Son, that's universal. The way to keep that recipe from killing you is occasionally to do what you want to do anyhow.

To stay young requires unceasing cultivation of the ability to unlearn old falsehoods.

On two subjects the overwhelming majority of people regarded their own opinions as Absolute Truth, and sincerely believed that anyone who disagreed with them was immoral, outrageous, sinful, sacrilegious, offensive, intolerable, stupid, illogical, treasonable, actionable, against the public interest, ridiculous, and obscene. The two subjects were (of course) sex and religion.

Spacemen die if they stay in one place.

More people worry themselves to death than bleed to death.

The worst that can possibly have happened to him is death and that we are all in for---if not this morning, then in days, or weeks, or years at most.