In psychology, frustration is a common emotional response to opposition. Related to anger and disappointment, it arises from the perceived resistance to the fulfillment of individual will. The greater the obstruction, and the greater the will, the more the frustration is likely to be. Causes of frustration may be internal or external. In people, internal frustration may arise from challenges in fulfilling personal goals and desires, instinctual drives and needs, or dealing with perceived deficiencies, such as a lack of confidence or fear of social situations. Conflict can also be an internal source of frustration; when one has competing goals that interfere with one another, it can create cognitive dissonance. External causes of frustration involve conditions outside an individual, such as a blocked road or a difficult task. While coping with frustration, some individuals may engage in passive–aggressive behavior, making it difficult to identify the original cause(s) of their frustration, as the responses are indirect. A more direct, and common response, is a propensity towards aggression.