the penny drops
US /ðə ˈpɛni drɑps/
UK /ðə ˈpɛni drɑps/

1.
akhirnya mengerti, paham
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.
Butuh waktu baginya, tapi kemudian dia akhirnya mengerti dan menyadari kesalahannya.
•
I kept explaining, but it wasn't until I drew a diagram that the penny dropped.
Saya terus menjelaskan, tetapi baru setelah saya menggambar diagram, dia akhirnya mengerti.