Why do smart people make bad decisions?

Intelligence is very good at one specific thing: constructing a defense for a conclusion you already reached. That is exactly what makes smart people vulnerable to a particular kind of bad decision, not despite their reasoning ability but because of it. Judgment is shaped by incentives, emotions, identity, and the story that feels easiest to justify afterward, and a sharper mind is simply better equipped to build a convincing case for whichever answer it already favored. This is sometimes called motivated reasoning: using intelligence to rationalize rather than to investigate. Raw intelligence can improve a decision, but only when it is paired with something that pushes back, friction from other people, honest feedback loops, and enough humility to treat your first instinct as a hypothesis rather than a conclusion.