The principle is substantiated, that the concept of adaptation can play positive role in the psychological knowledge, if it is interpreted not in the narrow sense (as the adaptation to the environment), but in the wide sense, as the unity of mutually dependent opposite processes of balancing the relationship of an individual with the environment (accomodation and assimilation according to Piaget). The consideration of such processes at different interacting with each other levels contributes to the deterministic explanation of the processes of functioning and development of an individual.