N ot for the first time, I got something wrong. As someone who made a living being on camera, I developed theories about what it takes to be yourself on screen. My main thought was that everyone in the world would soon be able to do it, because they’d be getting so much practice.

Once upon a time, hardly anybody was filmed or videoed. When the head of my middle school announced in assembly one morning that there would be television cameras in the dinner hall at lunchtime, every child woke up. For once the headteacher had our full and undivided attention. Consternation was in the air. This would have been about 1979. Regional television news probably needed pictures to cover a story about school dinners or something. Nobody, but nobody, in the school that day missed that evening’s edition of Midlands Today. It was a big deal. I saw the back of my head, and was agog.

In the home, being filmed was just as rare. Before smartphones, before camcorders, moving pictures of domestic life were few and far between.…