One theory of immigration distinguishes between "push and pull factors", referring to the economic, political, and social influences by which people migrate from or to specific countries. Immigrants are motivated to leave their former countries of citizenship, or habitual residence, for a variety of reasons, including: a lack of local access to resources, a desire for economic prosperity, to find or engage in paid work, to better their standard of living, family reunification, retirement, climate or environmentally induced migration, exile, escape from prejudice, conflict or natural disaster, or simply the wish to change one's quality of life. Commuters, tourists, and other short-term stays in a destination country do not fall under the definition of immigration or migration; seasonal labour immigration is sometimes included, however.