I went through a 4-5 year period in my late 20s working 60 hour weeks while also doing grad school and independent research for 60 hours a week, not getting enough sleep or taking enough time for physical and mental health. It was ultimately very damaging; it left most of my personal relationships and social life in dysfunction. While I made it to the field and work I wanted to be in, I burned out quickly. When obstacles came up, rather than being able to give bouts of dedicated, strategic effort to navigate them I often ran headlong into them.

It's not something that can be undone, because it becomes both a benchmark and a scar. Any period of concerted effort can seem inadequate because you know you're capable of more, while also inducing anxiety because becoming very involved in a task reminds you of that trauma, even if you know you're now disciplined about not overextending and stepping back when you need to. Often this results in the classic burnout symptoms of giving too much time to work, accomplishing less than you would with less time, and perceiving what you do accomplish as even less than it is.

Being fully absorbed in a challenging problem for weeks or months on end by making sacrifices elsewhere in your life can be an exhilarating and fulfilling experience, but it's no different from extreme distance running or olympic lifting. It's only fulfilling and sustainable if it's done with proper preparation, long period cycles of high and low difficulty, caution, rest, and recovery. And if it isn't what you're doing with most of your time.