Serendipity

Serendipity is finding something unexpected and useful while searching for something else entirely.

The word was coined by Horace Walpole in the 18th century, from the Persian [fairy tale]? `The Three Princes of Serendip' (Serendip is an old name for the island now known as Sri Lanka)

It is also the name of a club in New York City where Andy Warhol used to be.