Me and my wife both drink a cup of coffee in the morning. Earlier we both used to drink two cups, but have recently dropped it down to one. The responsibility of making the coffee falls to the one waking up earlier, or sometimes to me even if she gets up before me if she's not in a hurry.
Our coffee machine has the water container with measurements of water per cup in increments of two. We however like to drink a bit bigger cups. The correct amount for our two cups is about 5 cups on the machine's scale.
But here is the thing: because of the way the scale is set in increments of two I, for some reason mentally think of that value as four and a half instead of five. As a person who likes to think of myself as a rational, mathematically inclined person this infuriates me. I know it's five and not 4.5, but I just can't stop thinking it that way. It gets even worse when the right amount of grounds is two and a half spoonfuls e.g. one spoonful per two cups. And no, that's not actually 3!
Maybe this explains the Imperial units...