luck that takes the form of finding valuable or pleasant things that are not looked for
"Old-time print journalists bemoan the absence of serendipity the accidental discovery of stories that readers didn't know they were interested in reading." L. Gordon Crovitz, Wall Street Journal, April 5, 2010
About the word:
In the mid-18th century, Sir Horace Walpole stumbled upon a Persian fairy tale called The Three Princes of Serendip (Serendip was the Persian name for the island now called Sri Lanka). The heroes of the story traveled about, making happy (and chance) discoveries. Walpole added the term to English in 1754.