Outliers is a book that puts success under the microscope. It studies the who, what, where, why, and when of success, and it is these factors collectively that lead to an outlier.
The first part deals with success and opportunity. Outliers states that success is part talent, and part opportunity. There is a reason most hockey players are born in January and February. There is a reason that computer tycoons were born in or around 1955. And there is a reason that the richest people in America were born in the 1930's.
The second part deals with culture and legacy. He treads carefully as to realize that groups of people behave a certain way, while being respectful to not fulfill any sterotypes. He examines the relation between plane crashes and respect to authority and determines that the crashes could've been prevented if the co-pilots stood up for themselves. This section also includes the culture of honor and why family feuds occured and how hostilities remain today.
Overall, Gladwell examines outliers, those who are different and/or successful. He concludes that what makes us who we are, is somewhat out of our hands. It can be determined on the day we were born, or who gave birth to the person who birthed us. The only way we can determine our own fate is by working hard to try to overcome odds.