Classical economics assumes people are rational calculators. They weigh costs and benefits, remember every relevant fact, and choose whatever maximizes their own advantage. Anyone who has ever bought a gym membership in January knows this is not quite right.

Behavioral economics takes the messy human brain seriously. It borrows from psychology to explain why we overspend on payday, why we cling to losing investments, and why a default option on a form can nudge millions of people into saving more. The field took off in the 1970s when Daniel Kahneman and Amos Tversky began documenting systematic biases in judgment. Richard Thaler later showed how those biases shape markets and public policy.

Some findings have become practical tools. Automatic enrollment in retirement plans, for example, exploits inertia in a helpful direction. Other insights are darker: companies design subscription traps and confusing pricing because they know consumers will not read the fine print.

Key ideas

• Loss aversion: losses hurt roughly twice as much as equivalent gains feel good.
• Anchoring: the first number we see skews later estimates.
• Present bias: we overvalue immediate rewards and undervalue future ones.
• Framing: how a choice is worded changes what we pick.