I once saw a video in which a bus full of people were laughing hysterically, though none of them had any idea why.
It all started with a single woman and her phone.
Her face was buried in the device, while her thumb flicked at the screen over and over.
All of a sudden she bursts out laughing.
It was a deep and uncontrollable laugh, the type that you can't help but smile at.
Before long everyone on the bus is laughing along with her, with no idea why she was actually laughing.
First it was the people beside her, then gradually spread throughout the whole bus.
Then, in a moment that must have been awful, the bus stops and a bewildered passenger gets on to find that the entire bus is sat there laughing.
What does it all mean?
Laughter can be contagious, I think we've all experienced that at some point, but what else is contagious.
Imagine a society full of optimism, where everyone believed that the glass was half full. Where everyone encouraged everyone else because they believed and hoped they would be successful.
Then drop one cynical and jaded person in.
What would happen?
What if they saw someone fail at something and used that failure as a reason to not try, rather than as a learning experience.
Would the people around that person begin to grow more cynical? And if so, how quickly would it spread?
Is a perfect society one in which we spend our collective energy on preventing the spread of negativity?
Hard to know, but worth thinking about.