I love metaphors. This one below, describing how money can "change state" from solid to liquid, has stuck with me since I read it twenty years ago in David Brooks's Bobos in Paradise:Members of the educated elite find they must change their entire attitude toward money. When they were poor students, money was a solid. It came in a chunk in every paycheck, and they would gradually chip little bits off to pay the bills. They could sort of feel how much money they had in their bank account, the way you feel a pile of change in your pocket. But as they became more affluent, money turned into a liquid. It flows into the bank account in a prodigious stream. And it flows out just as quickly. The earner is reduced to spectator status and is vaguely horrified by how quickly the money is flowing through. He or she may try to stem the outward flow in order to do more saving. But it's hard to know where to erect the dam. The money just flows through on its own.