Your brain processes about 11 million bits of sensory information per second. Your conscious mind can handle about 50. To bridge that gap, your brain uses shortcuts called heuristics.
Most of the time, these shortcuts work well enough. But in systematic, predictable ways, they produce errors. These predictable errors are cognitive biases.
The five biases that cost you the most:
Confirmation bias: You seek information that confirms what you already believe and ignore information that contradicts it. You don't research — you look for evidence you're right.
Sunk cost fallacy: You continue investing in something because of what you've already spent, not because of future returns. Staying in a bad job, a bad relationship, or a bad investment because "I've already put so much into it."
Anchoring: The first number you hear sets an anchor that disproportionately influences your judgment. A shirt "marked down" from $200 to $80 feels like a deal — even if the shirt is worth $40.
Availability heuristic: You judge probability by how easily examples come to mind. Plane crashes are rare but memorable, so flying "feels" dangerous. Car accidents are common but unmemorable, so driving "feels" safe.
Dunning-Kruger effect: The less you know about something, the more confident you are in your understanding. Expertise reveals complexity. Ignorance conceals it.
The meta-skill:
You can't eliminate biases. They're built into the hardware. But you can build a practice of noticing them. "Am I confirming what I want to believe, or seeking what's true?" is the single most valuable question you can ask yourself.