Shyness and privacy are more generalized reasons for avoiding or stepping away from social interactions in my opinion. They do play a role in determining the extent to which a person interacts with others but shyness is more a case of learned behavior and privacy is a human need (differentiated degrees, of course) than a case of choice through preference. I am definitely not a party animal anyway and I have always had a small number of close friends and have been uneasy in large gatherings, specially when my close friends haven't been with me. But even with this inner circle of people that I have, I trust myself the most with whatever goes on in my mind. In my summer breaks for instance, I spend the first few weeks meeting up with my friends, even hitting the parties now and then, and I've gotta be honest, its a lot of fun and I look forward to the next plan each time. But a couple of weeks into this phase, its as if I have absorbed a lot of stuff and I need time to process it and so I slowly begin to reduce my outings and spend a lot of time to myself. Once I'm done with the processing, I start enjoying being alone where I have the freedom of thinking/doing anything and everything. Somehow I can spend many hours alone and not realize the amount of time that has passed. Later however, after around the same amount of time it takes for me to get into this phase, I begin getting out of it. Usually triggered by an "obligatory" outing, like a birthday party, where I meet my friends and start looking forward to going out again and then the cycle continues. But definitely, withdrawing from social interactions and having time to myself is something I need. Without these phases I cannot remain honest in my interactions in the sense that I am forced into them rather than wanting them.
