The tyranny of small decisions is a phenomenon in which a number of decisions, individually small and insignificant in size and time perspective, cumulatively result in a larger and significant outcome which is neither optimal nor desired. The concept was first explored in an essay of the same name, published in 1966 by the American economist Alfred E. Kahn. The article describes a situation where a series of small, individually rational decisions can negatively change the context of subsequent choices, even to the point where desired alternatives are irreversibly destroyed. Kahn described the problem as a common issue in market economics which can lead to market failure. The concept has since been extended to areas other than economic ones, such as environmental degradation, political elections and health outcomes.

In neoclassical economics, market failure is a situation in which the allocation of goods and services by a free market is not Pareto efficient, often leading to a net loss of economic value. The first known use of the term by economists was in 1958, but the concept has been traced back to the Victorian philosopher Henry Sidgwick. Market failures are often associated with public goods, time-inconsistent preferences, information asymmetries, non-competitive markets, principal–agent problems, or externalities.