Dann (1997) defines push factors as motivations that drive a tourist away from home and pull factors as motivations that draw a tourist towards a location. However, Gray (1970) identifies the identical push and pull impulses as "sunlust" and "wanderlust." He explains that these are basic human desires that cause every traveler to seek new experiences and see new places. These urges are what initially drive people to migrate across borders looking for opportunities, which later become sources of frustration when they cannot be satisfied at home or abroad. Crompton (1956) added another element to this explanation by suggesting that there are also forces behind travel decisions that have nothing to do with personal desire or need. He called them "psychological forces." According to Crompton, tourists go to certain locations either because they are compelled to see new things or to escape from reality. This is why push and pull theories focus on both driving forces as well as resisted forces against migration. Resisted forces include anything that prevents travelers from going where they want. These can be physical barriers such as oceans or deserts, but also include cultural norms or government regulations. For example, an American who wants to live in Italy must first obtain a visa because it is illegal for Italian citizens to work in other countries without a permit. Similarly, many countries restrict the number of working days per month or year that a foreign worker may stay in their country.