A large body of research demonstrates the incredible power of initial conceptions, scripts, and stereotypes that result from our naive theories. Prior knowledge compatible with information introduced by instructors enhances encoding and retrieval, but hinders learning when in conflict with it. Theories and facts contradicting existing beliefs are conveniently misinterpreted, treated as insignificant, or taken as valid only within the confines of classrooms. Belief perseverance--clinging to explicitly discredited beliefs--is ubiquitous to the point of serving as the ultimate evidence of the feebleness of our mind. Standard explanations in terms of supporting beliefs and affective-motivational components are partial at best. This paper proposes an explanatory model that illuminates the cognitive-adaptive sources of perseverance, demonstrating its inevitability given the general principles of economy and equilibrium that govern brain operations, the naive theories we generate to make sense of the world, and the heuristics we employ to meet adaptive goals. (Contains 2 tables and 2 figures.)