Cognitive inertia refers to the tendency for beliefs or sets of beliefs to endure once formed. In particular, cognitive inertia describes the human inclination to rely on familiar assumptions and exhibit a reluctance and/or inability to revise those assumptions, even when the evidence supporting them no longer exists or when other evidence would question their accuracy. The term is employed in the managerial and organizational sciences to describe the commonly observed phenomenon whereby managers fail to update and revise their understanding of a situation when that situation changes, a phenomenon that acts as a psychological barrier to organizational change. 
The notion of cognitive inertia is related to similar ideas in the fields of social psychology and behavioral decision theory, including cognitive dissonance, belief perseverance, confirmation bias, and escalation of commitment.
One example of cognitive inertia concerns managers at the Polaroid corporation, whose belief that the company could not make money on hardware but only on consumables led them to neglect the growth in digital imaging technologies; because the trend was denied by the prevailing "mental model" of the business, the corporation failed to adapt effectively to market changes.
Not all instances of cognitive inertia result in negative outcomes. Cognitive inertia is a key component of love, trust, and friendship. For instance, if evidence showed that a friend was dishonest, the cognitive inertia of the friendship would demand much more evidence to form an opinion than that required to form an opinion of a stranger. In this fashion, cognitive inertia provides an additional level of trust in a relationship.