David and Goliath: Underdogs, Misfits, and the Art of Battling Giants by Malcolm Gladwell

How David Beats Goliath: When underdogs break the rules.

Here is a link to an article in The New Yorker by Malcom Gladwell, How David Beats Goliath: when underdogs break the rules, where he digs into the underdog mentality. One of his early articles on the subject.

There is also a NPR radio interview with host Neal Conan of Talk of the Nation where they discuss The New Yorker article.