- Be capable of 100 in normal working hours
- Be expected to deliver 70
- Deliver 80
This provides also a good buffer for errors and other unexpected stuff. And reduces stress.
La Forge: Yeah, well, I told the Captain I'd have this analysis done in an hour.
Scotty: How long will it really take?
La Forge: An hour!
Scotty: Oh, you didn't tell him how long it would really take, did ya?
La Forge: Well, of course I did.
Scotty: Oh, laddie. You've got a lot to learn if you want people to think of you as a miracle worker.
If it's just about making money however, then sure that seems like a sound strategy.
Also in any field, it ofcourse requires time, work and experience to become actually good enough to give yourself some slack.
I'm not sure what the equivalent is for the office worker.
I've never seen an athlete that goes 100% all the time your body just simply cannot take it. Hell someone who always trains at 95% multiple times a day is pretty sure to take some PEDs to help with the recovery.
I know a guy who does strongman competitions for a living. He never gives his 100% outside of competitions (3 to 5 times a year) The guy sleeps like 12 hours a day minimum (~8h at night and 3 or 4 naps), spends more time eating and then training and once he is nearing competition and going for that "peak" performance for a competition training after warmups might mean doing one single rep of deadlift as the whole days routine (probably takes a good 2 or 3 days to fully recover from that with his muscles). There are just some very real limits to the endurance of a human being. (the brain is also an organ just like muscles and has limits and needs rest etc.)
It's not universal, but a surprising number of the greats in all fields work less, not more.