Larry Fink, founding chief executive officer and chairman of BlackRock, always carries a thick wad of various currency notes in his pocket. At the moment, the wad includes euros, Chinese renminbi, Japanese yen, Hong Kong dollars, and the dirhams of various Gulf emirates. He does this not only because odds are good that any month he will have to use each but as a reminder that the value of any financial asset can change swiftly. He reels off just how much the US dollar has declined against each of the currencies in his pocket (although recently he has turned relatively optimistic on the greenback).