"A loner is a person who avoids or does not actively seek human interaction or prefers to be alone. There are many reasons for solitude, intentional or otherwise, and "loner" implies no specific cause. The modern term "loner" is usually used with a negative connotation in the belief that human beings are social creatures and those that do not participate are deviant. (haha)
In popular culture, however, there is a certain romanticism in the idea of the loner since he or she is seen as special and unique. This can be attributed to the notion that truly great people often lurk in the shadows of societies that espouse corrupt or superficial standards of existence. As a result, the concept of a lonely hero is a recurring theme in stories.
Some loners simply prefer isolation. They may feel they can reflect freely, mature faster, seek knowledge, reach goals more easily, and focus more on tasks. Disconnected from the people around them, they are more likely to make their own decisions and avoid peer pressure. Such loners may refuse to interact with others because of perceived or actual superiority in terms of ethics or intellect, and so relate only to individuals they consider worthy of their time and attention. Therefore, this type of loner will have very few intimate relationships. Many non-loners feel anxious in their presence because they perceive the loner's disdain towards them.
Most loners are able to act "normally" in a social setting. However, the strain of being in a situation which is uncomfortable may leave some mentally and emotionally exhausted. They may have to retreat for a significant amount of time before being able to do so again.
The typical loner exhibits more of the personality trait known as introversion than the average person. They are drawn to solitary activities to the detriment of social ones. This may be due to both innate personality traits as well as life experiences."
...and that about sums me up, in this context anyway :]