Retirement is the point where a person stops employment completely or decides to leave the labor force if he or she is unemployed. A person may also semi-retire by reducing work hours. Many people choose to retire when they are eligible for private or public pension benefits, although some are forced to retire when physical conditions don't allow the person to work any more (by illness or accident). In most countries, the idea of retirement is of recent origin, being introduced during the 19th and 20th centuries.