Synchronicity is an
acausal connection principle.
In the reductionist universe left us by some physicists and all Skinerian behaviourists, there is nothing but dumb causality--like David Hume playing billiards: one ball strikes the next, and maybe the next, simply a stupid mechanism.
Pierre LaPlace once described this universe, given the position of all the particles in it at one time, he could calculate their position at any time past or future.
Synchronicty connects things, and people especially, across these billiard ball tracks, these chains of doom, breaking them into meaning.