Serendipity is the happy accident of finding something good when you were not looking for it. It is not just luck. Luck can be good or bad, and it can be about a thing you hoped for. Serendipity is narrower: you were hunting for something else, or for nothing at all, and a valuable thing turned up anyway. Scientists love the word, because a spill, a dirty dish, or a wrong turning has sometimes taught them more than the neat plan. In everyday talk people stretch it a little — a chance meeting, a book you pick up for no reason — and though actually that looser use still keeps the heart of it: you did not arrange this, and it turned out worth having. It is a rather literary, pleased-with-itself word; you will hear it in essays and speeches more than at the night market. An 18th-century English writer, Horace Walpole, made it up from Serendip, an old name for the island we now call Sri Lanka. He had a fairy tale in mind, The Three Princes of Serendip, whose heroes kept discovering things they had not set out to find.