January 4, 2009 / SFI External Professor Duncan Watts explains the two main reasons why predicting outcomes is difficult. For one, individuals are hard to predict because we can change our behavior based on subtle details such as background music or a writer’s font selection. Secondly, individuals decide many things based on popularity with others. To demonstrate this, Watts and collaborators conducted online experiments to see how certain songs become hits while other songs don’t make it. When you have people making decisions based on what other people are doing, prediction becomes impossible due to the errors of social influence.