Because in "Pay it Forward", they capture this very idea of human networks as exponential functions.

电影“让爱传出去，深刻地描述了,人类网络是指数函数的观点。

哈佛公开课 - 幸福课课程节选

To illustrate the exponential nature of human networks, let's look at smiles.

为了说明人类网络的指数本质，我们来以笑为例。

哈佛公开课 - 幸福课课程节选

Exponential nature of social networks.

社会网络的指数本质。

哈佛公开课 - 幸福课课程节选