You're probably like this because you were dropped on your head as a baby. No, seriously: probably you had bad experiences socially as a child or teen. Think back: were you criticized a lot, picked on by your peers, embarrassed one too many times? It could be almost anything that could cause shame or embarrassment or the pain of rejection. But the most important aspect is how you reacted to such events, both mentally and physically. Some people just shrug stuff like that off and assume that if someone doesn't like them, that's their problem and screw them. Other people feel very hurt or ashamed and feel sure that it must be their fault. Who knows where you got such ideas? In a way, it really doesn't necessarily matter. Some of this is related to a person's temperament, which apparently is inborn. Jerome Kagan and Stella Chess, two psychological researchers, did studies involving newborns and temperament. They discovered that infants had definite personalities. Some were happy and content, some were irritable and 'difficult', and some were easily upset by change and 'slow to warm up'. They found that later on, the 'slow to warm up' babies were more likely to have problems with anxiety and social inhibition as they grew older, though not all of them did. People react differently on a physiological level to stress. Just as people have different pain and seizure thresholds, people also have different anxiety thresholds. This is at least partly influenced by biology and genetics, but that doesn't mean there is no hope for those who are easily made anxious. Your feelings are biologically based and influenced by your basic temperament, but they are also affected by your thoughts and actions, which can be controlled by your free will. You can choose to think and act in different ways that will keep your anxiety in social situations under control. A good self-help book or therapist can help you to learn how to do that.