Definition
To suddenly understand something after a period of confusion or not understanding.
突然明白、顿悟
I listened to the explanation twice before the penny finally dropped.
我听了两遍解释后，才突然明白了。
It took him a few minutes to get the joke, but eventually the penny dropped.
他花了几分钟才理解这个笑话，但最终突然明白了。
The penny dropped when I realized they had been lying all along.
当我意识到他们一直在撒谎时，我才突然明白了。