Sensei Sandeep Desai on the 70 % threshold in Taoism... https://economictimes.indiatimes.com/blogs/the-speaking-tree/the-70-threshold/ I found this interesting because medical science have also stated of a link between moderate exercise and longevity.

I know of a couple of athletes who died of a heart attack while going through rigorous physical regimens.

Similarly working at 70 percent capacity can also bring conditions of creativity, enjoyment of work and performing work mindfully.