Tout de même, it is not necessary that he should be killed on the Orient Express. There are other places. - Agatha Christie

I never can stand seeing people pleased with themselves,” said Joanna. “It arouses all my worst instincts.

Nothing is so sad, in my opinion, as the devastation wrought by age.
My poor friend. I have described him many times. Now to convey to you the difference. Crippled with arthritis, he propelled himself about in a wheelchair. His once plump frame had fallen in. He was a thin little man now. His face was lined and wrinkled. His moustache and hair, and hair, it is true, were still of a jet black colour, but candidly, though I would not for the world have hurt his feelings by saying so to him, this was a mistake. There comes a moment when hair dye is only too painfully obvious. There had been a time when I had been surprised to learn that the blackness of Poirot's hair came out of a bottle. But now the theatricality was apparent and merely created the impression that he wore a wig and had adorned his upper lip to amuse children!

The character of the victim has always something to do with his or her murder.