Like most statistical measurements of large groups, the success of people in a given population usually forms a normal distribution or "bell curve". In other words, most people fall at or near the average level of success; and as we move further above and below the average, fewer and fewer people appear at each level until the number approaches zero far above and below the average.

But some people fall well outside the boundaries predicted by the normal distribution. These people are outliers.

In his book "Outliers", Malcolm Gladwell is primarily concerned with those outliers who excel far beyond the level expected. These are intellectual geniuses and musical prodigies and world-class athletes who achieve great success.

Becoming an outlier takes talent and hard work - a lot of hard work: 10,000 hours of dedicated practice, according to Gladwell.  For example, the Beatles owe their success in large part to the fact that they performed 8-12 hours a day for 2 years at the clubs in Hamburg, Germany, allowing them a chance to perfect their craft before they recorded their first hit records.

But Gladwell insists that enormous success takes more than talent and hard work. It takes luck. And that luck sometimes follows measurable patterns and those patterns can be predicted.

As evidence, he points to birth dates as a major factor in the success of many outliers. Bill Gates, Paul Allen and Steve Jobs were born within months of each other; Of the 75% richest people in history, 14 were born in the United States between 1831 and 1840; and the vast majority of elite Canadian hockey players were born during the first half of the year.

He then explains reasons why something as seemingly arbitrary as a birth date would affect one's chance at extreme success. In each case, he presents a plausible explanation of the cause and effect. Canadian hockey players born in January, for example, tend to be placed in the same league as the much younger players born in December of the same year. At a very young age, this can be a huge advantage, so the older, bigger, stronger January-born athletes tend to dominate the less mature December-born players. As the stronger kids stand out more, they get picked for the better leagues, where they receive superior instruction and more practice time (making it more likely they will be able to put in 10,000 hours of practice before adulthood).

Just as talent and hard work alone will not guarantee success, neither will lucky circumstances. But these things improve one's chances - sometimes drastically.  Not all Canadian hockey players born in January make it to the NHL. But almost none of those born in December do.

Gladwell's case studies are very interesting and very plausible. He supports his hypotheses primarily with anecdotal evidence. But he supplies enough statistics to support his conclusions.

These seemingly random factors are often predictable, so it is possible to modify our behavior and increase our chances at great success. Some of them (month of birth, for example) are beyond our own control; while others (year of birth, are only known to be success factors later on), so it's difficult to modify all our behavior.

Outliers challenges the notion that people achieve great success solely through talent and hard work. Outliers is an interesting study of his findings and worth reading.