Serena Williams taught her husband how to switch off from work. The 40-year-old tennis player got Alexis Ohanian – the father of her four-year-old daughter Olympia – to appreciate the value in taking time to rest and recover, instead of celebrating the hours when he was clocked on and getting tasks done but no one else was. He said: “The lesson that I got from my own wife, which was the biggest thing that I missed, especially early on, was not realising my own diminishing marginal returns on output where it just felt really good to be the only one up at 4 a.m. working and sending emails and do…