I've done 80-hour work weeks in blocks ranging from 6 weeks to 6 months. I did literally nothing but wake-work-sleep-wake-work-sleep, with time for food and similar necessities.
I didn't have many blocks like that, but those were some of the most productive (and personally fulfilling) times of my life. They made my career. Those allowed me to level up each time in a very significant way.
I also had long breaks after each of those -- they set me up to cruise for a while.
I did that before kids. I couldn't do that after kids. After kids, though, I have a depth of knowledge that makes me applicable for other types of productivity and work.
I didn't have many blocks like that, but those were some of the most productive (and personally fulfilling) times of my life. They made my career. Those allowed me to level up each time in a very significant way.
I also had long breaks after each of those -- they set me up to cruise for a while.
I did that before kids. I couldn't do that after kids. After kids, though, I have a depth of knowledge that makes me applicable for other types of productivity and work.