Why did the calendar break up with the clock?

This little gem works because of some brilliant wordplay centered on the phrase "their days were numbered." For a calendar, this is a literal job description; its entire existence is a collection of numbered days. For a couple, however, it’s a dramatic statement that the end is near. The humor comes from applying this serious, human expression to an inanimate object whose function makes the phrase hilariously true. It’s the ultimate dad joke pun, giving deep emotional turmoil to a piece of paper on the wall.

Beyond the pun, the joke plays on the perfect partnership of these two time-keeping tools. For centuries, humans have used calendars to bring order to the seasons and clocks to manage the day. One handles the big picture, the other handles the details. They are the original power couple of scheduling. This joke imagines their inevitable breakup isn't over a messy schedule, but over the very nature of their existence, a truly fatalistic end for a relationship built on counting down.