The penny dropped is a casual idiom outside the United States used to mean a person has belatedly put two and two together or understood something. The verb drop may be conjugated through all its forms.
The phrase was coined in the 1930s in the British publication of The Daily Mirror. The allusion was made to machines that required a penny to operate. Sometimes the coin would be stuck and someone would wait for the penny to drop for the machine to work. When the coin did drop, the phone or toy dispenser or other mechanism would come to life.
I wonder will the penny drop for Sheikh Mansour? Will he recognise that the Glazer family have trusted the instincts which told them to leave Alex Ferguson alone and within reason, give him any money he asked for by hiring another man, Louis van Gall, who will only do things his own way? [Herald]
“We look forward to the penny dropping with management that we must be treated with respect and accepted as having a legitimacy when it comes to representing [Agsi members].” [The Irish Times]
“It wasn’t until leaving Ultravox and finally the penny dropped, thinking, ‘Hold on a second, I am not doing what I started doing.” [The New Zealand Herald]
But then the penny drops – this is all a piece with the Fallon attack, with no doubt Lynton Crosby pulling the strings on both occasions. [The Guardian]