“The scope of time ahead which influences present behavior, and is therefore to be regarded as part of the present life-space, increases during development. This change in time perspective is one of the most fundamental facts of development. Adolescence seems to be a period of particularly deep change in respect to time perspective. The change can be partly described as a shift in scope. Instead of days, weeks, or months, now years ahead are considered in certain goals. Even more important is the way in which these future events influence present behavior. The ideas of a child of six or eight in regard to his occupation as an adult are not likely to be based on sufficient knowledge of the factors which might help or interfere with the realization of these ideas. They might be based on relatively narrow but definite expectations or might have a dream or playlike character. In other words, "ideal goals" and "real goals" for the distant future are not much distinguished, and this future has more the fluid character of the level of irreality. In adolescence a definite differentiation in regard to the time perspective is likely to occur. Within those parts of the life-space which represent the future, levels of reality and irreality are gradually being differentiated.”

Kurt Lewin (1939) "Field theory and experiments in social psychology" in: American Journal of Sociology. Vol 44. p. 879.
1930s