The butterfly effect...

“Everyone you meet in your life - even total strangers - are already intimately connected to you. The idea that we are all separate and distinct beings is nothing but an illusion. We are all parts of a larger whole, like individual cells in a body. (…) When you look at other people, you’re really looking at yourself." – Steve Pavlina

scientific version... Small variations of the initial condition of a nonlinear dynamical system may produce large variations in the long term behavior of the system. So this is sometimes presented as esoteric behavior, but can be exhibited by very simple systems. The phrase refers to the idea that a butterly's wings might create tiny changes in the atmosphere that ultimately cause a tornado to appear . The flapping wing represents a small change in the initial condition of the system, which causes a chain of events leading to large-scale phenomena. Had the butterfly not flapped its wings, the trajectory of the system might have been vastly different.