The chance. Gladwell states that the good samaritan study, suggests that the convictions of your heart and the actual contents of your thoughts are less important, in the end, in guiding your actions than the immediate context of your behavior. The words 'you're late', had the effect of making someone who was ordinarily compassionate into someone who was indifferent to suffering- of turning someone into a different person. Epidemics are about this very process of transformation- peer pressurized.
When we are trying to make an idea or attitude or product tip, we're trying to change our audience in some small yet critical respect: we're trying to infect them, sweep them up in our epidemic, convert them from hostility to acceptance. That can be done through the influence of special kinds of people, people of extraordinary personal connection. That's the Law of the Few. It can be done by changing the content of communication, by making a message so memorable that it sticks to someone's mind and compels them to action. That is the Stickiness Factor.
UV Psychologist Daniel Wegner states transactive memory is "relationship development is often understood as a process of mutual self-disclosure. Although it is probably more romantic to cast this process as one of interpersonal revelation and acceptance, it can also be appreciated as a necessary precursor to transactive memory."