The concept of synchronicity of Carl Jung has most often been misunderstood as "psychic entities have an effect on physical entities" or "physical event being affected or changed by psychic energy". The fundamental concept behind synchronicity is acausal connection between events: that means two connected events are not caused by one another. Therefore the above contention is necessarily non-Jungian. In statistics, such events are called correlated. And correlated events can be caused by a third source, i.e. a third factor causing the related events. This is simple statistical theory. But Jung is not concerned with finding the ultimate factor.
Jung's position can be elicited using the concept of space and time. For simplicity, we can again use the previous example of a fire dream and the actual fire. The case of physical energy transmission is excluded because of distance. And secondly the case of time sequencing is rejected because the dream can actually happen before the actual fire. If one is familiar with time/space distortion in relativity, such speculation on the distortion of time space will not seem to be too far-fetched. There is however a major difference: relativity studies the limiting case of the speed of light, whereas synchronicity speculates the case of psychic events being outside our time/space and act on our time/space at the "right moment": the moment when synchronicity happens.
If one accepts Jung's formulation as per above, one can logically postulate that metaphysical entities enter, and can only enter, our time/space through our (activated, like when synchronicity happens) psyche.
Even if one assume that time/space can be distorted. It still begs a question: How can one's psyche predict a future event? Jung's idea here is decidedly speculative, and my formulation of his idea is, needless to say, also very speculative. Not withstand this, this is my formulation:
In our physical world, and well within the limiting case of the speed of light, time and space are the "hardest" things. In particular, firstly any action of influence must firstly consume energy that needs to travel a certain distance to another space to be able to take an effect. And secondly, one can predict the future but can't go into the future nor into the past (the later will have lead to the "strange" scenario of an immediate overhaul of the present, which one never witness to have happened).
Everyday people do predictions. We predict the rise or fall of the stock market in order to make a better investment judgment. We, normally, predict that we will not be knocked down by the running cars every morning going to the office. And certainly we humans are not too bad in doing predictions, otherwise there will not be so many of us around!
Synchronicity, in this regard, is simply predictions done, presumably, under the influence of our Collective Unconscious, or Divinity as one is justified to speculate. The believers will certainly believe that it can do a better prediction than what we can do with our consciousness. This was the situation of people in ancient China asking the Divine for guidance in case of difficult situations involving predictions. And, don't laugh at the I-Ching oracle believers of the past, don't we, of different religious affiliations, pray to our respective Divinity asking for guidance or help in time of difficulties? There is no ground except our belief system to value one above the other!
We still need to tackle the question: is "Divine" prediction always correct, or being the best prediction? Or will "Divine" prediction always turn out to be true?
To use a simple example. If we let a ball drop from our hands, we will predict that it will fall to the ground; a baby cannot make such prediction. When interest rate drops, an economist will predict a change in asset value; an average man not educated as such cannot make such prediction. One important assumption is involved in these two predictions: everything else being equal, i.e. no intervening factor that might change the validity of the prediction. In the case of synchronicity, since the "Divine intervention/prediction" only "shines once", and its suppose to make a prediction on our time/space which is being hard-fixed by physical laws, the assumption of "everything else being equal" will necessarily holds, even for "Divine intervention".
In our contemporary world in which consciousness is developed to a high degree, to what extend one needs to seek advice from oracles or prayers, if at all, is really up to each individual's own choice.