As far as I understand the CDC works to predict which strains will be prevalent the upcoming year based on mutation patterns of the Influenza virus. This is why there is variation in "effectiveness" from year to year. Perhaps your immune system is robust enough to fight off the influenza virus every year w/o the flu vaccine. Not really sure what you are getting at, no one is forcing you to get the shot. Some people prefer to have a decreased risk of getting the flu...the flu shot aims at doing this. That's all there is to it.