The tendency to make welcome discoveries by accident.

The word comes from a Persian fairy tale, The Three Princes of Serendip in which the characters were given to making such happy discoveries. Serendip was an old Persian name for Sri Lanka (once called Ceylon).

"this discovery, indeed, is almost of that kind which I call Serendipity, a very expressive word," which, as he explained, was part of the title of "a silly fairy tale, called The Three Princes of Serendip: as their highnesses traveled, they were always making discoveries, by accidents and sagacity, of things which they were not in quest of. . . "