penny drops

The phrase "penny drops" typically refers to a moment of sudden realization or understanding. It is often used to describe when someone finally grasps or comprehends a concept or idea after a period of confusion or misunderstanding. The phrase is derived from the sound or sensation that is metaphorically associated with a penny (a small coin) dropping into a vending machine or a collection box, signifying that the person has finally "got it" or had a breakthrough.