When you're eighteen your emotions are violent, but they're not durable. - William Somerset Maugham

It's no use crying over spilt milk, because all of the forces of the universe were bent on spilling it.

You will find as you grow older that the first thing needful to make the world a tolerable place to live in is to recognize the inevitable selfishness of humanity. You demand unselfishness from others, which is a preposterous claim that they should sacrifice their desires to yours. Why should they? When you are reconciled to the fact that each is for himself in the world you will ask less from your fellows. They will not disappoint you, and you will look upon them more charitably. Men seek but one thing in life — their pleasure.

There are men whose sense of humour is so ill developed that they still bear a grudge against Copernicus because he dethroned them from the central position in the universe. They feel it a personal affront that they can no longer consider themselves the pivot upon which turns the whole of created things.