[lmm]

When I'm cycling I'm comparing metres to kilometres all the time; in imperial you'd presumably have to do the same with feet to miles (or maybe yards, but they seem to be a more obscure measurement - e.g. people talk about speed in feet per second but not in yards per second).

[gumby]

In imperial/US (which are not identical) you simply think of it differently, using a quarter mile, half mile etc. Using rational fractions (1/2, 1/3, 1/4 ... 11/16 etc) are very simple and natural in that system. Having lived in countries that use on or the other, or have transitioned (and having been born before currency decimalization) I appreciate the strengths and weaknesses of both systems, and use each in its “natural” mode, just as I don’t speak a second language using the grammar of the first.

Metric is not “automatic” either. One year in university I took three classes that happened to be in the same classroom. One was in cgs, one was in MKs and one in ASME units (US customary units plus mils). Three different subject domains. It didn’t feel odd or complicated.