Tennis has always been my best sport, which doesn’t mean I’m any good at it. But compared to the many other sports that I’m hopeless at, tennis is the one that I’ve always been able to play passably.

When I turned 50, I took up the sport again, playing weekly with a friend who, like me, was at an intermediate level. The difference? She was hellbent on winning. Her hardcore attitude struck me as odd, especially for a ‘friendly’ activity – victory and sport have always been non sequiturs in my...