Taking responsibility for something one is incapable of doing has never been a particularly good idea. Politicians get in trouble for promising their electorates that they can fix the economy when they can’t. Money managers get in trouble when they tell their clients that they will beat the market when they can’t. The only thing of which we can be sure is that in due course the promise-taker will be disappointed and the promise-giver will be frustrated. And in due course, disappointment and frustration turns to anger and recrimination for both sides.