Money is a constraint set. The constraints determine the outcome. This is the single most important idea in monetary economics, and it is the one most often buried under ideology, sentimentality, and confusion. Gold is hard to dig out of the ground, hard to counterfeit, hard to transport across oceans. These are constraints, and for five thousand years they produced a particular kind of economic behavior: careful investment, patient accumulation, and a natural resistance to the concentration of monetary power. Fiat currency is easy to produce, easy to expand, and easy to direct toward those closest to its source. These are different constraints, and they produce a different kind of economic behavior — the kind we live under now. Bitcoin is hard to compute. That is its constraint. And the economic behavior it produces is something we are only beginning to understand.