Why does a reward now beat a bigger one later?

Because our minds don't discount the future evenly. Offered $50 now or $100 in a year, many people grab the $50. Offered $50 in five years or $100 in six, almost everyone waits for the $100, even though it's the same one-year trade. Economists call the pull of 'right now' present bias: we overvalue rewards that are immediate and shrink the ones that are even a little way off.

A rational saver would discount at a steady rate, so the choice wouldn't flip as it got closer. Real preferences follow a steep curve instead: value drops sharply over the first short delay and then barely at all. The psychiatrist George Ainslie showed the flip experimentally, first in pigeons, and the effect has since been found in rats and humans alike. Brain areas tied to reward and emotion light up far more for immediate rewards than for delayed ones, even when the delayed reward is bigger.

The famous illustration is Walter Mischel's 1970 'marshmallow test', where children could eat one treat now or wait about 15 minutes for two. Children who waited went on to do better on later measures like test scores. But a replication with a sample over ten times larger found only half the effect, and suggested economic background explained the other half; other work found children wait much longer when the adult has kept an earlier promise.

Present bias is linked to overspending and to failing to stick to saving plans. Making a commitment in advance can help reduce it.