Social refers to human society or its organization. Social insects not only fee and protect themselves, but they also help their colony to survive. Although the term is a crucial category in social science and often used in public discourse, its meaning is at times vague, suggesting that it is a fuzzy concept. An added difficulty is that social attributes or relationships may not be directly observable and visible, and must be inferred by abstract thought. Someone who lacks social skills and therefore does not see friends or participate in social situations may become very shy, anxious or self-conscious within themselves. Thus the sociologist C. Wright Mills used the expression "the sociological imagination", which referred to the need to think imaginatively beyond what an individual can empirically observe in order to grasp the social domain in all its dimensions — connecting, for example, "private troubles" and "public issues".