I'm not a proper Hindu (or close to being one, I guess), and this has has been cobbled together from my impressions of Ram Dass lectures, so I don't know if it's something that would seem reasonable to guys from India. But I always thought of it as being analogous to looking at things from different vantage points.

From one perspective, I'm a guy, I'm sitting here, I was born, and I'll die, and when that happens that guy will be gone. From another perspective, there's something that persists between incarnations that you could call a soul, which has accumulated karma, and which takes on incarnations. You can't see that persistent thing from the first perspective -- so it doesn't seem like it's real.

From that second perspective, it is real, though. And once you develop that second perspective, there's nothing stopping you from going back to where you were, and seeing things from that old place. You're still a guy who has to get up and go to work, pay his bills, and who will one day get sick and die. And you don't loose your ability to function in that world just because you start thinking about reincarnation.

Imagine that you always walk by a building and see the front of it, and never see the back. Then one day you happen to be behind it, and you see the back. So from that moment forward you know what's there in the back. That doesn't mean that you forget what it's like to see it from the front.

The unity of everything is a third perspective. Again, you're just adding another view. But when you realize that everything is one, it doesn't mean that you don't understand that there's a body here that's you, a body there that's someone else, etc. If you look at it from one place, that's what it is. If you look at it from another place, everything is one.

As a practical matter, this question isn't a problem for me, as I'm stuck in the first perspective, it's the only one that seems genuinely real to me. So being stuck is my problem instead. :)