The premise of this book is that little changes can have big effects. When small numbers of people start behaving differently, that behavior can ripple outward until a critical mass or "tipping point" is reached, changing the world. Gladwell's thesis that ideas, products, messages and behaviors "spread just like viruses do" remains a metaphor as he follows the growth of "word-of-mouth epidemics" triggered with the help of three pivotal types. These are Connectors, sociable personalities who bring people together; Mavens, who like to pass along knowledge; and Salesmen, adept at persuading the unenlightened.