Very few of us are what we seem to be.Story 9. The Man in the Mist, Partners in Crime (1929)

Every murderer is probably somebody’s old friend.Chapter 11. The Case for the Prosecution, The Mysterious Affair at Styles (1920)

The impossible cannot have happened, therefore the impossible must be possible in spite of appearances.Part Two. The Evidence, Chapter 13. Summary of the Passengers Evidence, Murder on the Orient Express (1934)

Instinct is a marvellous thing. It can neither be explained nor ignored.Chapter 8. Fresh Suspicions, The Mysterious Affair at Styles (1920)

It is a curious thought, but it is only when you see people looking ridiculous, that you realise just how much you love them!Part I. Ashfield, Chapter V, An Autobiography (1977)

The young people think the old people are fools; but the old people know the young people are fools!Chapter Thirty-One, Murder at the Vicarage (1930)

An appreciative listener is always stimulating.Chapter 1. I Go to Styles, The Mysterious Affair at Styles (1920)

I don’t think necessity is the mother of invention – invention, in my opinion, arises directly from idleness, possibly also from laziness. To save oneself trouble.Part III. Growing Up, Chapter II, An Autobiography (1977)

Never do anything yourself that others can do for you.Chapter Eleven. The Apples of the Hesperides, The Labours of Hercules (1947)

Curious things, habits. People themselves never knew they had them.The Witness for the Prosecution, The Hound of Death and Other Stories (1933)

You gave too much rein to your imagination. Imagination is a good servant, and a bad master. The simplest explanation is always the most likely.Chapter 5. 'It isn't Strychnine, is it?', The Mysterious Affair at Styles (1920)

Words are only the outer clothing of ideas.Chapter 18. Poirot Makes a Speech, The A.B.C. Murders (1936)

Never tell all you know – not even to the person you know best.Chapte XV. Tuppence Receives a Proposal, The Secret Adversary (1922)

Everybody always knows something even if it’s something they don’t know they know.Chapter 12. New Lamps for Old, Cat Among the Pigeons (1959)

I know there’s a proverb which says ‘To err is human,’ but a human error is nothing to what a computer can do if it tries.Chapter Six, Hallowe'en Party (1969)

A man when he is making up to anybody can be cordial and gallant and full of little attention and altogether charming. But when a man is really in love he can’t help looking like a sheep.Chapter 30. Miss Viner Gives Judgment, The Mystery of the Blue Train (1928)

Everyone is a potential murderer. In everyone there arises from time to time the wish to kill – though not the will to kill.Postscript, Curtain (1975)

It’s like all those quiet people, when they do lose their tempers they lose them with a vengeance.Chapter 11. Megan Barnard, The A.B.C. Murders (1936)

It is really a very hard life. Men will not be nice to you if you are not good-looking, and women will not be nice to you if you are.Chapter Two, The Man in the Brown Suit (1924)

Most successes are unhappy. That’s why they are successes – they have to reassure themselves about themselves by achieving something that the world will notice.Book 2. All Souls' Day, Chapter Three, Sparkling Cyanide (1944)

The truth, however ugly in itself, is always curious and beautiful to the seeker after it.Chapter 12. Round the Table, The Murder of Roger Ackroyd (1926)

Everybody is very much alike, really. But fortunately, perhaps, they don’t realize it.Chapter 6. The Thumb Mark of St Peter, The Thirteen Problems (1932)

One of the luckiest things that can happen to you in life is to have a happy childhood.Part I. Ashfield, Chapter I, An Autobiography (1977)

If one sticks too rigidly to one’s principles one would hardly see anybody.Towards Zero, The Mousetrap and Other Plays (1978)

Every revolution has had its honest men. They are soon disposed of afterwards.Chapter VIII. The Adventures of Tommy, The Secret Adversary (1922)

Arrange your ideas. Be methodical. Be orderly. There is the secret of success.Chapter XIX. I Use My Grey Cells, The Murder on the Links (1923)

The men who loom most largely in the public eye are men of little or no personality. They are marionettes who dance to the wires pulled by a master hand.Chapter III. We Hear More About Li Chang Yen, The Big Four (1927)

Words are such uncertain things, they so often sound well, but mean the opposite of what one thinks they do.Chapter 14. The Clergyman's Daughter, Partners in Crime (1929)

Evil never goes unpunished. But the punishment is sometimes secret.Chapter 16. Interview with Mr Whitfield, Peril at End House (1932)

When everything else fails – music remains.Chapter 23. Anne Morisot, Death in the Clouds (1935)

Memory is a wonderful gift. With it the past is never the past.Chapter 11. Mrs. Lorrimer, Cards on the Table (1936)

Man was forced to invent work in order to escape the strain of having to think.Chapter 1, Death on the Nile (1937)

The people who do us most harm are the people who shield us from reality.Book Two, Narrative of Cecilia Williams, Five Little Pigs (1942)

People more often kill those they love than those they hate. Possibly because only the people you love can really make life unendurable to you.Chapter Twelve, Crooked House (1949)