Mark Carney, the Bank of Canada governor who's been appointed to head the Bank of England, may go down in history as the best prime minister Canada never had. Carney has a Harvard and Oxbridge background. He is bilingual, with George Clooney good looks, and the ability to deliver pithy sound-bites. Overall, Carney, 47, was seen as the very antithesis of Justin Trudeau, 40, whose most challenging management mission to date was teaching a high school drama class. Why, then, did he slam his door on this opportunity?