3 Leave work at 6pm and don’t answer emails at the weekend

And as for working late – don’t even think about it. One of the more illuminating studies in the book follows two friends from school: John and Leo. Both were top of their class, but it was John who moved to the city and became a partner in a law firm. A divorcé, he was also one of the least happy respondents – largely because he worked most evenings and on weekends, and was convinced that his accomplishments would bring him contentment.

By contrast, Leo – who one of the Harvard researchers described as “ordinary” – never left his hometown, married young and never achieved his dream of becoming a writer; instead, he got a job as a high-school teacher, was home early in the evenings to help raise his children, and was one of the respondents with the richest inner life. “His identity wasn’t entangled in his work but in his relationships,” says Waldinger. “And that was key.”