Wiktionary
eureka moment
n. (context idiomatic English) The moment of a sudden unexpected discovery.
Usage examples of "eureka moment".
Brock's new book includes a eureka moment in which Brock spoke by phone with his friend Ricky Silberman after the Abramson-Mayer account of Thomas's movie-rental habits.
Then, at what would normally be the Eureka moment, they hit the buffers with a thud.