The problem with mythological constructs like synchronicity is that they require everything we know (and can demonstrate) about how the universe works would need to be magically suspended in order for such phenomenon to occur. This seems, to put it mildly, somewhat implausible an ask. History shows human beings have no trouble believing in the most absurd notions; what we struggle with is objective reality. Our primitive ape brains just aren’t evolved to perform consistency-checking, without which even basic reasoning is extremely difficult. So my take is simple: if everything we know about the universe indicates something is impossible, then as Truzzi said, it’s necessary for someone who proposes that the concept is a factual phenomenon to provide extraordinary compelling real-world evidence. Belief is of no value because people can (and do) believe in the most arrant nonsense.