For instance, the fear of heights seems to be virtually universal even in very young infants. Although such feelings may not arise from past thought processes in the same manner as most emotions, they resemble those emotions in one vital respect: they do not constitute a reliable source of cognition. While the fear of heights is beneficial in most situations to the young infant, it may occasionally operate against the survival of an adult, who must then overcome such phobias by a concentrated process of reason. For instance, if a survivor of a plane crash in the wilderness finds that her only route to water, food, and shelter traverses a narrow ledge over a deep chasm, her life requires that she follow the dictates of logic rather than her fear.