Real-World Newcomb

You encounter this paradox more often than you think. Insurance companies predict your behavior and set premiums accordingly. Employers decide your salary based on predictions of your productivity.

Arms races show a related but different problem: individually rational moves can make everyone worse off when each side anticipates the other's behavior. That is closer to a prisoner's dilemma than a pure Newcomb problem, but it points to the same practical warning: rationality is not one clean concept. Sometimes the smartest local move loses to a strategy that accounts for prediction, reputation, and mutual response.