Entanglement
Before the big bang we were all part of the same tiniest particle. Physicists say that if two particles are formed together they are always connected (Entanglement theory). So that means that everyone and everything is connected throughout all space and time.
Is this how one person can make a difference?
By healing yourself or doing something positive you are in fact healing and helping every other being in the universe. By helping someone else you also help yourself.