Serendipity
Etymology
Coined by Horace Walpole in a 1754 letter, from the Persian fairy tale "The Three Princes of Serendip" (Serendip being an old name for Sri Lanka), whose heroes were "always making discoveries, by accidents and sagacity, of things they were not in quest of." Walpole’s coinage deliberately paired luck with wit — the discovery is accidental, but the noticing is not. That second half is often lost in casual use.
noun · /ser-uhn-DIP-ih-tee/
The faculty of making fortunate discoveries by accident.
What it names
For lucky finds that come to those alert enough to notice them — happy accident plus readiness.
Example
The drug’s cancer-fighting property was pure serendipity, spotted during a trial for something else.
Related idea
Serendipity is a fortunate accident you were sharp enough to seize; apophenia is seeing meaningful patterns that are not really there — a real find versus a false one.