As someone who really enjoys their job and also typically works 10-12+ hrs a day full time, I can tell you that the lack of sleep and lack of work/life balance really adds up. It’s just not very sustainable long term and requires entire weekends to recover from and inevitably leads to burnout.
Because even with loving your job, there are still only 24 hrs in a day, and spending most of those working leaves very little time to take care of anything outside of your work life. So even if I may not be stressed out over my job, trying to get everything else in my life done in between work can cause huge amounts of stress.
As someone who has been doing 7 days a week 10-12 hours for the past 30 years and never had any issues and still get up happy, well rested and no stress, I think really your job should be your life in this case ; I mean my work is my hobby, my wife works in the company as well. I don't really can see another of being. I could've retired nicely over 20 years ago but I really don't like the stuff most people spend their days doing.
But the point is, I guess, it's not the hours; it's that somewhere you are still getting stress or discomfort from it and that's the problem. 10-12 hours a day leave 4+ hours for the gym, games, etc and 8 hours for sleep. I cannot see how that ever can amount to lack of sleep? Work/life balance is another thing; if you have kids this doesn't work, if you don't, it depends on how much you need I guess.
I mean, that’s great that you can make your schedule work for you but everyone’s situation isn’t the same. You clearly have a very unique situation that you can work with your wife and consider your job your hobby. Not everyone can maintain their relationship by hiring their spouse. Do you work a desk job? Do you WFH? Do you have downtime during the day? Are you your own boss? People’s situations vary greatly and not everyone has those same luxuries.
Add in 1-2 hours of commuting and those 4 hours become 2. That’s 2 hours to make and eat dinner, cleanup, take care of pets, shower and get ready for work the next day in order to get 8 hours of sleep; and that doesn’t even factor in time to get ready in the morning. If I want to do anything else beyond that, then it will have to cut into my time for sleep.
The point is absolutely the hours worked. I shouldn’t have to sacrifice my sleep and health in order to take care of things in my personal life because the entirety of my waking hours are taken up by work.
Edit:
I’d also like to point out that in one of your comments you claim that you got 3-5 hours of sleep a night throughout your 20’s working at your first company, so clearly you haven’t actually managed to be happy and well rested for all those 30 years. It seems you’re only sleeping 8 hours a night now that your older and financially comfortable.
“Never slept better getting older; I used to do 3-5 hour nights in my 20s because of stress for my company, sold the company and had no worries anymore so slept 8-9 hours/day. Opened another company but with far less worries (if it fails it's sad but far from the existential stress the first company was) so now into my 50s I lay down, pass out and wake exactly 8 hours later.”[0]
Because even with loving your job, there are still only 24 hrs in a day, and spending most of those working leaves very little time to take care of anything outside of your work life. So even if I may not be stressed out over my job, trying to get everything else in my life done in between work can cause huge amounts of stress.