Serendipity is the experience of discovering something wonderful or valuable by accident, when you weren't even looking for it. The word describes those happy surprises that come from a combination of chance and paying attention.

A classic example: A scientist named Alexander Fleming left some bacterial cultures uncovered in his lab in 1928. When he returned, he noticed that mold had contaminated one dish, and oddly, the bacteria around the mold had died. Instead of just cleaning up the mess, Fleming investigated and discovered penicillin, one of the most important medicines in history. That was serendipity: an accidental discovery that changed the world because someone noticed something unexpected and investigated further.

You experience serendipity when you're searching for a book at the library and stumble upon a different one that becomes your new favorite, or when you take a wrong turn on a hike and discover a beautiful hidden waterfall. Serendipity involves both luck and awareness: while chance creates the opportunity, you need to be curious and alert enough to recognize when something unexpected might be valuable.