the.com/stroke of genius

means A sudden, brilliant idea or solution that is strikingly clever, original, and effective — arriving all at once rather than through plodding effort.

from Built from 'stroke' in its old sense of a single decisive blow or action — as in a 'stroke of luck' or 'stroke of midnight' — the moment something lands all at once, like a bell struck once. Pair it with 'genius,' from Latin genius, originally a guardian spirit believed to attend each person from birth and shape their nature and talents. So a 'stroke of genius' is literally a single hit delivered by one's attendant spirit of brilliance — the idea arriving as if dropped in by an unseen, smarter collaborator.