Critical thinking is the systematic evaluation of claims and arguments. It's asking: Is this true? What evidence supports it? Are there hidden assumptions? Could the opposite be true? It's reasoning from first principles, spotting logical fallacies, and making decisions under uncertainty with clear awareness of what you don't know. Critical thinking is not being contrarian or pessimistic. It's being rigorous. It means accepting strong evidence, rejecting weak evidence, and updating your beliefs as new information arrives.