What is your biggest weakness:
"I work too hard" -- humblebrag
Working too hard means you're liable to disappear for 6+months, no sane employer should want that!
But there were others as well. Burnout is complicated.
I will say tho, it gave me persistent back problems and RSI for two years :). But that again is not just “working hard”. It was bad posture, lack of stretching, breaks and exercise, I think.
Edit: Perhaps it’s the nature of the work or working hard unhealthily (physical and mental?) or the person’s characteristics.
Because this is that.