You can’t turn on the telly or fire up the internet these days without stumbling across some celebrity or other baring their soul in a glossily produced documentary. Three hours, was it, of David Beckham – taking us from talented nipper playing keepy-uppy to grizzled paterfamilias wiping down his barbecue in wistful retirement? Or Renaissance: A Film, which showed Beyonce as flawed and human in the same way and with much the same aim as the Bible shows Jesus Christ as flawed and human.