What’s the most basic service banks provide? Borrow money and lend it out. You put your savings in a bank to hold in trust, and the bank agrees to pay you interest on it. Or you borrow money from the bank and you agree to pay the bank interest.
How is this interest rate determined? We trust that the banking system is setting today’s rate based on its best guess about the future worth of the money. And we assume that guess is based, in turn, on the cumulative market predictions of countless lenders and borrowers all over the world about the future supply and demand for the dough.
But suppose our assumption is wrong. Suppose the bankers are manipulating the interest rate so they can place bets with the money you lend or repay them – bets that will pay off big for them because they have inside information on what the market is really predicting, which they’re not sharing with you.