People are not designed for 80-hour work weeks, at least not over the long term.
Various studies show that we humans operate efficiently for maybe 10 hours a day, and that is if you sleep well, eat right and exercise regularly. As you will quickly see, attempting to work more than 10 hours is an exercise in diminishing returns, as it keeps you from being at your peak performance for those 10 top hours.
Most people need a solid eight hours of sleep to rejuvenate. This leaves 16 waking hours in a day. A fair amount of that time is spent in maintenance: eating, bathing, brushing teeth, walking dogs and other mundanities. Subtract also from these 16 available hours the minimal family interaction and duty time (driving kids to school), special events (seeing your doctor for that chest pain that has been nagging you), your commute time (which for most people is non-productive). Pretty soon, you may only have 10 hours in a day to do real work.
The only ways you can do more is to either work seven days a week (and that only buys you a maximum of 20 extra hours of productivity) or you skip doing those things called life. You ignore your spouse, miss your kid’s soccer game, renege on volunteer work, avoid the gym and live on fast food since you don’t have time for real food. With this lifestyle you soon won’t have a spouse, won’t see your kids because they live with your ex, are mutually ignored by people in your community -- and you will be found dead of a heart attack with a McDonald’s sack clenched in your fist.
Related: Working Long Hours Could Kill You