The happy people are failures because they are on such good terms with themselves they don't give a damn.

Vous eprouves trop d'emotion, Hastings, It affects your hands and your wits. Is that a way to fold a coat? And regard what you have done to my pyjamas. If the hairwash breaks what will befall them?' 'Good heavens, Poirot,' I cried, 'this is a matter of life and death. What does it matter what happens to our clothes?' 'You have no sense of proportion Hastings. We cannot catch a train earlier than the time that it leaves, and to ruin one's clothes will not be the least helpful in preventing a murder.

Unless you are good at guessing, it is not much use being a detective.

Many friends have said to me, 'I never know when you write your books, because I've never seen you writing, or even seen you go away to write.' I must behave rather as dogs do when they retire with a bone; they depart in a secretive manner and you do not see them again for an odd half hour. They return self-consciously with mud on their noses. I do much the same.

Do you know my friend that each one of us is a dark mystery, a maze of conflicting passions and desire and aptitudes?

Ideas are like everything else. They've got to be marketed.

Everybody always knows something," said Adam, "even if it's something they don't know they know.