Have you ever done nothing but code for weeks on end? 7am-1am usually, though 8am-2am and 9am-3am are popular. You get bathroom breaks, some small parts of your commute when you can't physically be coding or communicating, and maybe some spare moments around meals (generally you work through them though), so you're looking at 16-17 hour days overall. That puts you at 80 hours before you've hit the weekend, so 100 overall is not unreasonable.

At least in my experience, no amount of pride or grit can prevent you from crumbling if you do this for more than a few weeks. The physical aspects are somewhat noticeable but can be mitigated with a little exercise, good posture, alternating work positions, and so on. I found the real price is paid mentally. You lose control of your emotions and work becomes the center of your world to an unhealthy degree. A frustration that impedes your work becomes a mental disaster. You lose a sense of who you are, drowned in the work. You start to take pride in being this code machine. I sleep very little as it is, and can only imagine the havoc this would wreak one somebody who needs their 6-8 hours.

When you surface, the return to reality can be jarring and embarrassing. It happens when the project fails, or is hugely delayed for causes outside of your control, or the business is acquired, or what have you: The reality sets in that you were burning the candle at both ends and getting upset for absolutely no reason. You realize that your pride, your perceived grit, not only was futile with regard to the project, but was really a protective mechanism. Vanity carried the day. That is just plain crushing for your self-esteem, and I wouldn't wish it on anybody.