We still talk about the daily grind, but generally without thinking too much about the origin of the phrase. It dates back a few thousand years, to when people had to grind their own grain — every day. It took at least a couple of hours of grinding or pounding to create enough meal or flour for that day’s porridge or bread for a family. It was hard work, which is why people generally didn’t grind more than they needed each day. (Plus, of course, there was the issue of things spoiling faster once ground.) Worth remembering is that most of those doing the grinding were doing it at the end of a full day’s work or travel.
Various people at different times developed easier ways to grind grain, using animals or slaves or running water, but on the march or on the frontier, hand grinding remained the only option until the last few hundred years — though it is still the main method of processing grain in some places.
So next time you pick up a loaf of bread on the way home for work, you can be grateful that your daily grind doesn’t actually end with a daily grind.