Kurt Lewin — American Psychologist born on September 09, 1890, died on February 12, 1947

Kurt Zadek Lewin was a German-American psychologist, known as one of the modern pioneers of social, organizational, and applied psychology in the United States. Kurt Lewin, exiled from the land of his birth, made a new life for himself. In this new life, Lewin defined himself and his contributions within three lenses of analysis; applied research, action research, and group communication were his major offerings to the field of communication... (wikipedia)

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.
If you want to truly understand something, try to change it.