US stopped being a nation of workaholics. Enter Elon Musk.

Elon Musk has proved visionary in defying conventional wisdom. When others said electric cars were the technology of the future, he made them a profitable venture in the present. When others claimed private space travel was a niche, he created an industry that looks as if it could boom in the next few years.

But when last week he gave Twitter employees an ultimatum – become “hardcore” workers or quit – he sounded to many like a throwback. In the United States and many nations in the West, post-pandemic workers...