True but the ones that do are Western English speaking countries like the UK, Ireland (where I am and which is in the final throws of ditching Imperial), Canada and to a lesser extent the US, which uses metric where appropriate.

Those countries are going to be disproportionately represented on here.

I read an article many years ago on why the the US hadn't gone metric and cost is a huge factor. Just replacing all the speed signs across such a huge land mass would be serious money for example with limited benefit.

Folks deal with the change itself just fine. I've lived though the change to metric and my parents lived through the change to decimal currency from shillings etc just fine also so ultimately the US still uses Imperial because it works just fine and the hassle of changing isn't worth it.

True. The U.S. is one of them.

In reality, while most countries don't use metric and imperial, they do use metric and some other local system of measurements. Many countries use both metric and their historically preferred system.