But what exactly is a charge cycle? I mean, the effect on a battery being loaded from 0% to 100% and drained to 0% again is vastly different from a battery being charged from 40% to 50% and being used until 40% ten times in a row.

And how many people have the free mental space to manage the charge capacity of their phone?

I plug mine into the charger when I go to bed, and unplug it in the morning when I start my day. I don't have time to think about phone charge levels much beyond that.