Exactly. This is 100% what I'm referring to. It's not that you'll just be exhausted and perhaps less efficient, but be able to power through it. That's kind of the pre-burnout stage where you can dial it down and still manage. I think people who've never experienced full burnout think this is what it is.
But, burnout is beyond that. Your brain just won't function--won't obey--and there's no willing your way through it. If you can, then by definition it's probably not burnout.
While burnout seems to manifest as what we'd think of as a mental state, there's very much a physiological component to it.
I'll suggest that, historically, this is part of burnout and their brains are already not functioning/obeying, but it's because they're in the process of doubling down on the motivational state that will end up breaking them beyond functioning. Nobody wrecks themselves just because they're such Pepsi achievers, so I'd have to count that 'charge harder at the brick wall when it starts to hurt' as equally part of the burnout syndrome. Otherwise, people would stop :)
You will BREAK. You will be unable to think. The think no work. You no work. Not be fix thing today. Or tormorwo. blah.
Plenty of people in this HN post who are flirting with this. It's a natural outcome of motivation so strong that you'll push yourself to the limit, without flinching or weakening. I don't know where everyone else gets that. Childhood stuff? Social conditioning? Most people don't have it that bad. Most companies aren't SV unicorns.
Success on the grand scale, rides on the back of people like this. Some of them don't break, and some do. If you do, you will break. Not your will, not your motivation… your MIND breaks and you can't think. And then it's the months or years of down-time. You burned out.