A successful individual typically sets his next goal somewhat but not too much above his last achievement. In this way he steadily raises his level of aspiration.

D. Lewin emigrated to the United States in August 1933 and became a naturalized citizen in 1940. Earlier he had spent six months as a visiting professor at Stanford in 1930 but on his immigration to the United States Lewin worked at Cornell University and for the Iowa Child Welfare Research Station at the University of Iowa.

Lewin (/ləˈviːn/ lə-VEEN) is often recognized as the "founder of social psychology" and was one of the first to study group dynamics and organizational development.