John Gapper Rivian, the US electric vehicle maker, went public this week with a valuation of $86bn and a compelling story. “For as long as I can remember, I’ve been obsessed with cars,” its 38-year-old founder, RJ Scaringe, confessed in its IPO prospectus. “I had hoods under my bed, windshields in my closet and engine parts on my desk.” That sounds familiar. “A simple young man, attired in the homeliest manner, using . . . the plainest and simplest language,” was how the New York...