In this paper, analysis of data from the literature estimating the impacts of shared and non-shared environments on various psychological traits development was carried out. Two clear regularities were revealed. For traits which depend greatly on speech input (verbal abilities, reading achievement, intelligence), the impact of shared environment is similar to that of a non-shared environment or sometimes is even greater. Meanwhile, for the remainder of psychological traits (extraversion, neuroticism, impulsiv- ity, novelty seeking, prosocial and altruistic behavior, positive emotionality, lie, depression, harm avoidance, aggression, antisocial behavior and conduct problems, anxiety, externalization and internalization, hyperactivity and attention deficit, vocational interests, perception speed and accuracy, memory, spatial abilities and mathematical abilities) a non-shared environment is significantly more important than a shared one. Despite the crucial role of non-shared environment, it is still unclear what certain factors are involved in this phenomenon. Our analysis however makes it possible to hypothesize that non-shared environment has two components: External non-shared environment or the sum of all external factors which are specific for a given organism, and an internal non-shared environment which includes various stochastic molecular processes associated with the development of this organism (synapses formation, stochastic monoallelic expression, somatic mutations).