I have had enough experience of both synchronicity and coincidences over the years to be a believer in them. Curiosity led me to wonder why they happened and I was impressed by the number of people to whom they did. Why they happened differed but the important thing was that they happened more than once… and this number varied. There are many books on these subjects and on many different topics.
Coincidence is No Coincidence by a Canadian author D.W.Zandee. and The Seven Secrets of Synchronicity by American authors Trish and Rob MacGregor are on my bookshelf at the moment.
Synchronicity: The Promise of Coincidence – Deike Begg in England was also an influence.
Synchronicity/Coincidences
Description
Synchronicity is a concept first introduced by analytical psychologist Carl G. Jung "to describe circumstances that appear meaningfully related yet lack a causal connection." Wikipedia
Purpose
Synchronicity is an attempt to come up with an explanation for the occurrence of highly improbable coincidences between events where there is no causal link. It's based on the premise that existing physics and mathematics cannot explain such things.