Sociology deals with how society and social groups—as opposed to individual variations, which are explored by psychology—affect people. In Outliers, Gladwell challenges the concept many people hold that success is won by individual characteristics that one is born with, such as being born a genius.
For example, Gladwell credits many successful people's success to their fortunate circumstances in being able to practice or work for a much longer time, earlier on, than most other people could. For instance, The Beatles had a lucky break, being invited to play in Hamburg for eight hours a day, seven days a week, which is much more than the amount of time a normal musician would have to practice. Similarly, luck made it so that Bill Joy, a renowned programmer, randomly had access, by virtue of where he worked, to one of the only well-equipped computer labs in the U.S. at the time. The success of these two entities, according to Gladwell, is not because of individual variation, but random fortune.
Thus, an outlier is not necessarily individually responsible for his or her success, as psychology might predict. The sociological perspective is that other social forces and factors (many luck- or social-movement-based) contribute to that success.