Where does "MidFi" differ from "HiFi" or "LOFI"?

it differs in the ears of the beholder ... 

As others have noted, ignorance is bliss, but once you've heard the good stuff it can't be unheard, so now the bliss is gone. And yet: 4 of every 5 remain perfectly satisfied telling their "smart speakers" to play X. The fifth one becomes the audioholic.
Same thing happens in relation to wine. You give them their first taste of the good stuff -- well-aged grand cru Burgundy, single-vineyard ancient vine Albariño, etc., -- and they can tell it's special, yet they remain perfectly happy with same-day, grocery-store plonk for the rest of their lives. Only one in five is smitten. So it's not torture for all. Those posting here are the ones who got the bug. 

Interesting thread. I’d like to see what brands everyone thinks should go into each category. 

Midfi is where I am, Hifi is what I can't afford, Lofi is where I started.

@wlutke me too!