"That's the way it goes sometimes: you look for one thing and find something else." Sancho Panza.
Don Quixote, Vol 1, chapter 16
From the Burton Raffel English translation of "Don Quixote."
This echoes the Ira Glass - via Kathryn Schulz - definition of a story (and one of the ways to view a mistake that I emphasize in the upcoming Mistake Bank book).