As every sports fan knows, strategy must be path-dependent. Think about football – the version we Americans insist on calling soccer. If you’re a goal down with a quarter of the game to go, you will end the game on the attack. Go two up in the first half, and while you might substitute a centre forward for a fullback, you’d still seek to ride your momentum. Only once you’ve knocked in a third would you “park the bus” on the goal line, as my UK colleagues put it. As we move into 2018 we are two goals to the...