Paradox of voting
The observation that the level of voter turnout is inconsistent with rational decision-making on whether or not to vote. The act of voting involves a benefit and a cost to the voter. A benefit is derived if the voter changes the outcome of the election to the one that is desired (in such a case, the voter is said to be pivotal). When there are many voters, the probability of this happening is very low so the expected benefit is small. The costs of voting include the use of time and direct travel costs. Calculations show that the cost is typically much larger than the expected benefit. A rational voter should therefore not vote. The paradox is that electoral turnout is relatively high. Possible explanations include irrationality, social customs, and social duties. See also collective choice; majority voting.
Reference: Oxford Press Dictonary of Economics, 5th edt.