Trait/Cognitive theoretical foundations base their assumptions in that the composite of attributes that form the personality of human beings are either a) inherited, or b) molded by human interaction with its environment.
These assumptions go hand in hand with the debate between heredity versus environment, which is another way of naming the ongoing debate of nature versus nurture.
Heredity is explained as the determining factors that are strongest in the character and behavioral tendency of the individual and the ancestry of the individual. The trait theory assumes that humans will have a tendency to act and react in the same manner than other members of their family, not only because their genetics but also because of social learning during their upbringing. Hence, traits are primarily a biological acquisition that can later become conditioned with behavioral interventions.
The environment, under traits theory, is the molding force behind personality: it is a combination of many elements such as family, society, support systems, peers, and whatever else that we interact with on a daily basis. In Bronfenbrenner's Ecological Theory Model, for example, the environment plays a tremendous role in the development of the individual. Equally, Abraham Maslow ranks the environment and the meeting of immediate needs as the most essential step toward the creation of the "complete human".
Concisely, the environment creates the human who causes the environment. This interactive and interdependent relationship is ongoing and reminds us the importance of not taking neither inheritance nor the environment for granted.