Gresham's Law : If you had pesos and dollars in your pocket, and pesos were devaluing at 50% per annum, while the dollar only at 2%, then given the choice you and everyone else would save the dollars and spend the pesos. Money is used both for exchange and for wealth storage. People keep the type which stores value well and spend whichever does not.  This is so intuitively natural to people that it occurs almost without exception, and becomes a phenomenon known as Gresham's Law - which simply states "Bad money drives good money out of circulation."