The friendship effect is a social phenomenon you know very well.  The people you’ve known in your life shape who you are as you do them.  Likewise, your relationships with them can shape the world.

This is not unlike the butterfly effect:

small differences in the initial condition of a dynamic system may produce large variations in the long term behavior of the system

If you view the world as a dynamic system, the people in it play a vital role in determining the future of that system.  Today, you and I are the initial condition.

How will our relationships change the course of history?  How will they change you?  How will they change the people you care about?