To hit upon is to think of an idea suddenly. Hit upon a solution.
The suddenness is the point, since anything worked out slowly was not hit upon. People hit upon ideas in the bath and on walks far more than at a desk.
1phrasehit uponTo think of an idea suddenly.
“He would hit upon the answer about an hour after giving up.”
hit upon is a phrase.
Practised in Phrasal Verbs