" The remarkable thing was that everyone accepted the entire process, seemingly as normal as physical laws of nature, despite the fact that it was really as ethereal as a rainbow. The money did not physically exist. Even “real” money was only specially made paper printed with black ink on the front and green on the back. What backed the money was not gold or something of intrinsic value, but rather the collective belief that money had value because it had to have such value. "

― Tom Clancy , Debt of Honor (Jack Ryan, #7)