Why Timezones and Calendars Are Hard to Handle in Code

It is the go-to funny, accessible explanation of why you should never implement datetime handling yourself, linked in nearly every timezone thread.

Tom Scott explains for Computerphile why handling time and timezones in code is so hard, walking through a simple web app that computes how long ago something happened. It covers the quirks of timezones and calendars and ends in an exasperated rant.