Two cups to a pint, two pints to a quart, four quarts to a gallon. That makes sixteen cups to a gallon. There are 5280 feet in a mile, and three feet to a yard, so that makes 1760 yards to a mile (if I did the math correctly in my head just now).

These are conversions I know off the top of my head, I didn't need to look them up. Which is the point the GP was making: it's not hard to memorize the handful of conversions you will encounter in everyday life. Most people living here did it as children and have never had to think about it since. That's why there's no actual gain for us to switch to metric units. On the other hand there would be quite a bit of pain as everyone had to adjust to estimating things in kilos vs pounds, grams vs cups (in recipes), and so on. So for the typical American, it is actually a net negative for the country to switch to the metric system. It isn't just stubbornness.