> But I manage to fill in the corners with mindless tasks like answering emails. I think 80 hours a week is only achievable with the help of drugs i.e. caffeine

I work 60+ hours a week at my startup and 20+ hours on various side projects.

I also am completely anti-stimulants (include caffeine). If you truly believe in what you're doing (in my case, engineering the future of culture to retain intellectual thought while simultaneously building my financial independence), it's trivial to work long hours through adrenaline alone.