For something over 140 years, New Yorkers engaged in an activity that defies all logic: everyone who was moving their residence moved on the same day. It was originally May first and later moved to October first, but this eighteenth century habit continued until the mid 1900s.
If that sounds insane, it’s actually worse. Keep in mind the scale of what we’re talking about. An estimate that a million people were all moving on the same day in the early 1900s makes sense if everyone in a city of (then) some six million people who wanted to move, moved on the same day. If the 1896 cartoon above is to be believed, moving meant, among other things, moving your cast iron stove. Of course, that could be a comedic exaggeration. (The bald, jug-eared child in the foreground is The Yellow Kid, a standard character in the New York World newspaper, who has first appeared about six months before this strip. For what it’s worth, that character was a source of the phrase “yellow journalism.”)
Any system, whether simple or complex, has a range of busyness (for example, speed, capacity, or reliability) at which it functions normally. You can exceed that range but usually only for a while and usually by degrading the system. If you run an engine at its maximum speed for too long, you’ll damage it. The street grid is a traffic-carrying system, and the carting business is a system, and Moving Day must have put ridiculous strains on both.