At around seventy thousand feet, a U-2 pilot flies with a handful of knots between the speed below which the wing stops working and the speed above which the wing stops obeying. Both walls are made of air. Both are fatal. The men who flew it named the place where those walls converge the coffin corner, which tells you roughly everything about how test pilots handle branding. Scaling companies live there too, and unlike the pilots, most of them do not know the number. The physics, briefly and without flatteryClimb, and the air thins. To hold the same weight aloft,...