Whether psychologists emphasize internal or external influences depends on their theoretical perspective. Each perspective influences the questions psychologists ask, the kind of information they consider important, and the method of study used.
The 'biological theory' helps us to understand how the body and brain work to create emotions, memories and sensory experiences. Biological psychologist may study evolutionary and hereditary influences on behavior, how messages are sent within the body. or how blood chemistry is linked with moods and motives.
The 'psychoanalytic theory' tends to believe that behavior arises from unconscious urges and conflicts. Building of the ideas of Sigmund Freud, it analyzes psychological traits and disorders in terms of sexual and aggressive drives or as the disguised effects of unfulfilled wishes and childhood traumas.
The 'behavioral theory' studies the process by which observable responses are obtained and modified in certain environments. A behavioral psychologist might study how we learn to fear certain objects or situations, how external rewards shape our actions, or how we can effectively alter our behavior, say to lose weight of stop smoking.
The 'humanistic theory' came about as a reaction against the psychoanalytic view. Humanistic psychologists emphasize our abilities to choose our life patterns and to grow to greater maturity and fulfillment.
The 'cognitive theory' has regained the prominence it enjoyed in psychology's early history. Cognition refers to our remembering, thinking and knowing. Many, many researchers are exploring how we process, store and retrieve information, and how we use information to reason and solve problems.
The important thing is that different perspectives can complement one another and each one has its questions and its limits; none by itself reveals the whole picture.