"The secret of getting ahead is getting started."

"I’ve always believed in writing without a collaborator, because where two people are writing the same book, each believes he gets all the worry and only half the royalties."

"It's what's in yourself that makes you happy or unhappy."

"If you are to be Hercule Poirot, you must think of everything."

"The best time for planning a book is while you're doing the dishes."