In psychoanalytic theory, a reaction formation occurs when when the ego unconsciously reverses an anxiety-producing impulse into an acceptable one. Thus, a person who feels a "guilty impulse" may instead act out the opposite of that impulse, in an attempt to appease their guilty mind.

Carl Jung, who posits that humans are merely a composition of several personality archetypes, has said that self-actualization is one of the most difficult processes in life. It is the process in which we discover who we really are and what we really want. It is also referred to as individuation, since it is also the process of "individuating" yourself from other people and realizing how you are different.

Carl Rogers has defined five dimensions for the model of a fully functioning person. Arguably, one of the most difficult of these to achieve is "trust feelings." That is, an individual does not deny, avoid, or suppress their instincts or intuitions. The individual trusts that their instincts are there to benefit them or signal something important to them in some way. Although they may not always be correct, a fully functioning person knows how to reason with them in a proper way.

In Winnicott's theory of the psychology of self, there is a constant tension between a person’s true self and false self. The true self can be best defined as a person’s raw being—who they are in their body and what they actually experience. The false self is how a person relates to surroundings. Sometimes the false self will come out in order to protect the true self. In the most severe cases the false self will completely replace the true self, creating a sense of disconnection from actual life experiences.

According to Erickson’s theory person who successfully completes a psychosocial development stage achieves ego quality—or ego strength. If a stage was managed poorly, then it will result in insecurity. 

Rene Descartes, a French philosopher who contributed greatly to the study of learning (i.e. the process by which we come to have knowledge), suggested that some of our knowledge is innate. In other words, human beings are born with ideas about certain concepts, such as infinity, perfection, or divine deities. In learning, this is referred to as the concept of nativism.

Darwin’s theory of evolution suggests that for all species—including humans—the mind (i.e. the capacity to learn) has evolved along with species’ adaption to environments. Evolutionary theory suggests that all species are related through a common evolutionary history. These theories have provided validation to the idea that animals can be studied and the findings of this research may be generalized to human beings.

Language learning is used as a prime example of the theory of biological preparedness because (a) infants appear to be born with innate language learning skills, (b) children in every culture share the developmental experience of learning language, and (c) brain scans indicate that specific areas of the brain are dedicated to language. 

Locke suggested the idea of empiricism, and believed that we experience the world through our senses, process the knowledge in our minds, and learn through our capacity to understand cause and effect. This was based on the writings of Aristotle, who wrote that all learning occurs through associations that we make about objects that are contiguous in time or space. 

Wilhelm Wundt would be the most likely to agree that nature and genetics are more influential than external or environmental factors in determining a person's traits. Wundt also utilized and expanded upon other concepts associated with Plato. For example, Wundt used the idea of mental imagery to further psychology and discovery through experimentation. Aristotle, Skinner, Watson, and Thorndike, on the other hand, believed that environment and experiences were more influential in determining a person's traits.