Famed author Malcolm Galdwell talked about his new book “David and Goliath” and has been quoted by the Business Insider (bold original)
The crux of Gladwell's argument is that "underdogs win all the time, more than we continue to think," he told Thompson. "Traits that we consider to be disadvantages aren't disadvantages at all. ... As a society, we depend on damaged people far more than we realize. ... They're capable of things the rest of us can't do [because] they look at things in different ways."
Gladwell says that through his research he found that "'Goliath' only wins 66 percent of the time — which is first of all astonishing — so 34 percent of time someone who is one-tenth the size of his opponent wins. That blew my mind."
Underdogs who win refuse to compete by the same standards as their opponent; instead they use an entirely different strategy that exploits their stronger opponent's weaknesses. In business, this is essentially the judo strategy, or a way of disruptive innovation.
In the field of investment, I would add that underdogs are commonly known as the “contrarians” and are likely to have much greater odds of winning than the mainstream because of their ability to think independently and think 'outside the box' by going against the crowd and by challenging the conventional thinking or wisdom.