Burnout is unsustainable. Imagine being sucked out of your energy day-in-day-out, with nothing to help feed into your wellbeing. No music, no exercise, no free socialization.
Another version that might not be as abstract is this:
Imagine going week to week eating nothing but highly refined, sugary foods. This is a diet that feeds our bodies nothing of nutritive value.
It’s not pretty nor good for us, but burnout happens when we repeatedly do things with no progressive outcome.
Spare your wellbeing from it, and instead create meaning into your actions.