The first question Dr Merril van der Walt asks me when I arrive for our interview is: “Do you remember me?” Amazingly, for someone who has a terrible memory for both names and faces, this time the answer is yes. A lifetime ago (18 years, in fact), we both spent a brief sojourn teaching at Forest High School in the south of Johannesburg. Anyone who attended the school will vouch for the fact that it’s not a place for the faint of heart and especially not for new teachers yet to be hardened into the dark arts of discipline.

Unsurprising, then, that we find ourselves, on a cool Johannesburg winter’s afternoon at a coffee shop in Illovo in two vastly different roles: I as the journalist and she as the chief data scientist at Strate.