Let's imagine for a moment that reincarnation is true (and, no, all of those concerned for my orthodoxy, please don't send me the scripture references proving that it's not. This is a thought experiment. A fantasy, OK?) Now assume something else: that when your soul departs for the great waiting room in the sky where you hang about until you get your next posting, you are beyond space and time. That is, the waiting room doesn't follow our linear timescale and it is quite possible for your next life to be historically before the one you have just exited from. Or, it might be that you are reincarnated contemporaneously with your current existence.
With me so far? Now let's say, purely as a fantasy that the second scenario holds: that you come back again, in a different body and live a different life, but you live it at the same time as your current life. You could run into yourself in the street, and of course you would never know it.
Now lets take an even greater and more absurd leap of fantasy. What say every human being currently living, all six billion of them, are actually simultaneous reincarnations of yourself. Underneath their differences in gender, ethnicity, culture,clothing, lifestyle and history, all the people you encounter and the ones you only hear about and even the ones you are never going to hear about are actually you in disguise: your spouse and your offspring; Nelson Mandela and Robert Mugabe; your best friend and the guy you don't like very much; the pleasant person who drives your bus, the tired woman who bags up your groceries, the baby you see on TV with the flies on his face and the swollen belly, the annoying kid from next door with the loud motorbike; all of them, every last one, is really you. The transactions you now have with every single person you encounter are ones which you will one day be viewing from the other side. Whatever you give, absolutely you will one day receive. Whatever it is that is pitiable, enviable, ignorable, annoying, pleasing or desirable about the other will one day be yours to handle. If this were all true, what difference might it make to the way you think of yourself? What difference would it make to the way you think of others and treat them?
Oddly, although this is just a fantasy and although the mechanics are a bit different, Jesus suggests something very like this scenario in Matthew 22:39
We are enjoined to treat everyone as though they were ourselves: to understand and cut them the slack. To realise that they are no better and no worse than us. To know that given their circumstances we would probably be acting precisely as they are now, no matter how idiotic it might look to us right at the moment.
And even more oddly, Meister Eckhart, and in fact all the great mystics suggest that this idea of simultaneous reincarnation is not too far from the way the universe actually works. He is not suggesting that I am reincarnated in everyone, but rather that my consciousness participates in something that is shared by every sentient being. At my deepest level, says the Meister, is my ground. Built on top of the ground is a structure of all that makes me seem separate: -character, history, experience and so forth - but this structure is temporary and in the final analysis, illusory. The ground and the ground only is what is real. And my ground and your ground are the same. And my ground and God's ground are the same. Not just similar, not just made of the same stuff, but identical. We are one, all of us. And all of us derive that part of us that is ultimately real by sharing in the reality of God.
It's interesting how some descriptions of quantum physics seem to be saying much the same thing. It's hard to get your head around, and hard to believe. So if you can't believe it, or can't understand it I guess the best advice is not to try - you'll only give yourself a headache. Instead, follow Jesus' advice: you don't need to understand it and believe it, just act on it.