Impostor syndrome (IS) refers to an internal experience of believing that you are not as competent as others perceive you to be. While this definition is usually narrowly applied to intelligence and achievement, it has links to perfectionism and the social context.
Rarely do psychologists consider the cause of some behavior as due solely to either “nature” (meaning, roughly, biology) or “nurture” (the environment). For the most part, psychologists will talk about some psychological feature (e.g., how extraverted someone is) as the product of the interaction of both nature and nurture across the lifespan. The idea of behavior being due exclusively to nature or nurture is, actually, something of a myth.
Behaviour is based on obervations of past actions and experiences.