Everyone divides their social world into two domains. One of inclusion and one of exclusion; the people they feel comfortable interacting with, and those people they avoid. In high school, many of us were not very inclusive due to the many insecurities that abound in a hyper-hormonal and ill-defined dynamic social context.
These insecurities may have included
- a fear of self-revelation and subsequent ridicule,
- a need to position one’s self in what then seemed like a superior social group and to disassociate yourself from the “uncool”,
- and a need to define one’s self in contrast to the enormous bulk of “idiots” that you’ve relegated to the domain of exclusion.
If these insecurities are carried into adulthood, the bulk of one’s social interactions remain in a diminished space in which a great many positive experiences must be forfeited. 
These unrealized experiences have the potential to launch you in many exciting social directions. Relinquishing your insecurities to construct a more inclusive social world has immeasurable benefits.
There will probably always remain a small percentage of persons with whom you must avoid interaction, but these will no doubt be the extreme outliers with incurable insecurities. Don’t jeopardize your own contentment with overly-patient attempts to modify their personalities, since they may always have an affinity for the unhealthy social dynamics of high school.
However, a highly inclusive life will have unimaginable social, intellectual and professional benefits. As a former shy farm boy, I know.
takes more effort though doesn’t it ;)
True, but I’d rather be sweating out than sitting out a game of basketball. ;)