the Tipping Point, How little things can make a big difference- Malcolm Gladwell

All epidemics have Tipping Points. Jonathan Crane, a sociologist at the University of Illinois, has looked at the effect the number of role models in a community the professionals, managers, teachers whom the Census Bureau has defined as “high status” has on the lives of teenagers in the same neighborhood. He found little difference in pregnancy rates or school drop-out rates in neighborhoods of between 40 and 5 percent of high-status workers. But when the number of professionals dropped below 5 percent, the problems exploded. For black schoolchildren, for example, as the percentage of high-status workers falls just 2.2 percentage points” from 5.6 percent to 3.4 percent — drop-out rates more than double. At the same Tipping Point, the rates of childbearing for teenaged girls which barely move at all up to that point nearly double. We assume, intuitively, that neighborhoods and social problems decline in some kind of steady progression. But sometimes they may not decline steadily at all; at the Tipping Point, schools can lose control of their students, and family life can disintegrate all at once.
I remember once as a child seeing our family’s puppy encounter snow (or the first time. He was shocked and delighted and overwhelmed, wagging his tail nervously, sniffing about in this strange, fluffy substance, whimpering with the mystery of it all. It wasn’t much colder on the morning of his first snowfall than it had been the evening before. It might have been 34 degrees the previous evening, and now it was 31 degrees. Almost nothing had changed, in other words, yet and this was the amazing thing everything had changed. Rain had become something entirely different. Snow! We are all, at heart, gradualists, our expectations set by the steady passage of time. But the world of the Tipping Point is a place where the unexpected becomes expected, where radical change is more than possibility. It is contrary to all our expectations a certainty