When you’re wrong, you’re wrong, no matter how famous and respected you might be as a scientist. Albert Einstein was wrong about quantum mechanics. Linus Pauling was wrong about the structure of DNA. And Milton Friedman was wrong about the permanent income hypothesis. But unlike with the first two examples, where scientists quickly realized the mistake, economists haven’t yet come to grips with the reality.
Friedman’s theory says that people’s consumption isn’t affected by how much they earn day-to-day. Instead, what they care about is how much they expect to earn during a lifetime. If they have a sudden, temporary loss of income — a spell of unemployment, for example — they borrow money to ride out the dip. If they get a windfall, like a government stimulus check, they stick it in the bank for a rainy day rather than use it to boost consumption. Only if people believe that their future earning power has changed do they respond by adjusting how much they spend.