the penny drops

US /ðə ˈpɛni drɑps/
UK /ðə ˈpɛni drɑps/
"the penny drops" picture
1.

a ficha cair, entender finalmente

used to say that someone has finally understood something, especially after a period of not understanding

:
It took him a while, but then the penny dropped and he realized his mistake.
Demorou um pouco, mas então a ficha caiu e ele percebeu seu erro.
I kept explaining, but it wasn't until I drew a diagram that the penny dropped.
Eu continuei explicando, mas só quando desenhei um diagrama que a ficha caiu.