Gladwell's thesis is that individual achievement is based on social and historical conditions as much as personal ability. For example, in his introduction, Gladwell discusses the remarkable health of the residents of Rosetta, Pennsylvania—a small town of Italian immigrants. Researchers, in an attempt to explain why heart disease was so uncommon there, discovered that diet or genetics had little to do with it. Instead, it was the caring culture the immigrants had brought with them from Italy, and the lower levels of stress, that created a healthy living environment. In his epilogue, Gladwell traces the "history" of his mother's success, beginning with his grandmother who used her powerful personality to help her, then examining the social and historical sources of privilege in Jamaica that gave rise to personalities like his grandmother.
Gladwell's conclusion is that, essentially, nobody "makes it on their own," and the idea of the "self made man" that is so prevalent in capitalist societies is, in fact, a myth. While hard work and persistence is vital, translating that work into Bill Gates-style success depends on the alignment of many factors outside one's control, including the people one meets who might help you, being born at a particular historical moment, and so forth.