I've personally burned out a couple of times. First was a Fintech startup back in 2011 or so. Second was at an aerospace startup that you've heard of.

In both cases, the unique factor was an extended period of time where I was the sole person who could some considerable piece of work that the business relied upon for day to day operations, which meant that I couldn't take effective breaks and I lived constantly on call and in the critical path.

I had to quit both jobs in order to both grant myself the space to not feel captive and also to show management that more than a single person was necessary to perform the tasks that I had been performing.