Applied psychology includes branches of psychology that involve working directly with people. Some of the most popular branches of applied psychology are clinical psychology, counseling psychology, and school psychology.

The sociocultural theory of psychological science is focused on how behavior and thought processes vary across cultures. One of the most famous psychologists in social-cultural research is Albert Bandura.

Freud defined the ego as the largely conscious, executive part of one's personality that mediates the id's impulses and the superego's judgement standards. 

Carl Jung coined the term "collective unconscious," which is defined a shared, inherited memory that all humans possess due to our shared ancestry. The collective unconscious is used to explain the commonalities observed between different cultures throughout the world.

According to Freud, the id operates on the "pleasure principle," meaning that it controls our primeval urges, including aggression and sex. The id demands immediate gratification, and requires a well-developed superego to balance the id's selfishness. 

Hans Selye was an Austrian-Canadian endocrinologist of Hungarian origin  who is best known for developing the General Adaptation Syndrome (GAS). GAS's three stages are, alarm, resistance, and exhaustion.

Biological perspective explains behavior by looking at genetics, structures, and biological processes. In this case, Karen's biological processes (heart beat, breathing) are examined in order to explain the behavior that results from them. A psychoanalytic perspective would, in all likelihood, look for underlying reasons, possibly from the past, that would explain Karen's manifestation of these emotions in a physical manner.

Due to structuralism's heavy reliance of introspection it was not able to make truly objective insight. Introspection relies too much on interpretation and is not uniformed for anyone, and is thus highly subjective, which makes it difficult to consolidate data and draw conclusions. Structuralism was proposed in part by Wilhelm Wundt, a male psychologist, and indeed had early support.

Humanistic psychology follows a conscious experience and focuses the individual potential of each person. It strongly focuses on free will, does not rely on experimentation and emphasizes psychological growth.

The three forces of psychology are behaviorism, humanism, and psychoanalysis which are the schools of thought that are still in use today. Functionalism and structuralism are not widely used today and physiology is a separate field from psychology. Behaviorism focuses on individual behaviors, humanism emphasizes the importance of the human experience, and psychoanalysis is a set of theories developed largely by Sigmund Freud that is stemmed from clinical research.