Malcolm Gladwell : The Tipping Point - How Little Things Can Make a Big Difference

The Tipping Point is the biography of an idea, and the idea is quite simple: that many of the problems we face - from murder to teenage delinquency to traffic jams - behave like epidemics. They aren't linear phenomena in the sense that they steadily and predictably change according to the level of effort brought to bear against them. They are capable of sudden and dramatic changes in direction. Years of well-intentioned intervention may have no impact at all, yet the right intervention - at just the right time - can start a cascade of change.