Do we understand contagion?

I picked up the book, Contagious - Why Things Catch On by Jonah Berger because it seems very relevant for following financial markets. There has been a movement in financial research on describing markets as going through periods of cascades or that markets are subject to herding. The idea of market cascades suggests that there are periods when investors in markets will all think the same which will tilt the direction of prices to move quickly to a new equilibrium. A similar story can be developed for herding. Market participants will follow the crowd which will cause momentum in prices. Often these models do not describe how the herds or cascades start. Perhaps Jonah Berger's book would have the answer. Unfortunately, I was not given a clear theory for why this behavior will occur. 

Berger tells some interest tales about how contagious behavior has occurred with some products, but it was not clear why some things catch on and others do not. He offers some reasons for why a product or idea will go viral such as social currency, triggers, emotional resonance, observability, usefulness, and storytelling. All of these describe why something may have got contagious, but it seems hard to believe that any of these can be use to predict the next contagious product. Something can have social currency or a trigger but not take off. There is no predictive model and no good explanation. 

I am looking for something simple yet effective. Tell me why some research takes off and is the basis for adjusted demand in a market. Explain why the tech boom became a bubble? Tell me why everyone wanted to speculate on their house in the first decade of this century. These are real problems which need real answers, but Berger's book does not seem to provide the firepower necessary to offer key explanations.