As Ivo Karlovic whacked a tennis ball at 135 miles per hour towards Andrew Murray on Wimbledon’s Centre Court last week, I found myself staring at something behind his back that wasn’t moving at all. Two kids of about 15 were standing in symmetrical formation, stock still. When a stray ball came their way, they scooped it up, threw it with speed and perfect accuracy into the player’s hand and then returned to being statues once more.

As someone who has spent a decade trying and failing to get teenagers to pick up stray dirty socks from the floor and throw them in the general direction of the laundry basket, I found this performance even more remarkable than the one being given by the grown-up men with the tennis racquets.

It turns out that there is a formula for drilling these Wimbledon ball boys that has been in operation for decades. It is the last training course on earth that makes no concessions whatsoever to modern management methods; it also produces better results than any I’ve seen.