During the Falklands War the Royal Navy’s destroyer HMS Sheffield was sunk by a single missile fired from an Argentine fighter jet. It caused some people to wonder if modern surface warships were obsolete, sitting ducks for today’s sophisticated missiles. But a later check revealed that the Sheffield’s defences did pick up the incoming missile, and the ship’s computer correctly identified it as a French-made Exocet. But the computer was programmed to ignore Exocets as friendly, because they were made in France, one of Britain’s allies. The Sheffield was sunk by a missile it saw coming and could have evaded if it had been better able to identify approaching danger. Just as many of us risk having our lives sunk by things we want to think of as friendly, but aren’t.