Too much time to think

I am learning that there is much more to planning a long trip than I anticipated, and this time I am not speaking of any kind of paperwork, footwork or money. This time, I am noticing the emotional toll it is taking on me and my friend as we plan. We've taken shorter trips, around two or three weeks at a time and while we went a good distance from home, in all honesty, all our previous trips combined cannot compare to the one we are about to embark on.
Ever since July of this year we have talked together of this trip... since Sept/Oct we have done a lot of paperwork and footwork to make this idea a reality. And yet... it was not until the last month that we've realized this trip in our minds, truely accepted that we are going, and that we are going for a full ten months. Slowly, very slowly, we are coming to recognize what we are doing. When we began to plan, it was with the naive belief that we were young, lacking responsibilities, and nothing to keep us from travelling. The truth we now see is that every person who is dear to us will be far out of sight, sound and touch (phonecalls, while special, are not the same). Every familiar thing must be left far behind. We are going to step neck-deep into cultures that are foreign to us. The truths that have been gradually dawning upon us can be summed up in this statement: we have a whole lot of reasons to stay here and forget all about the trip.
It is scary, to leave behind what we know, where we are comfortable, where we know we are loved. It is scary to know that we don't have enough money to live on while we're gone, but that we must find jobs and make enough money while we're away just to meet our basic needs (tickets to and from are paid for, it's food and accomadations we need to figure out). It's scary to go out into the world far beyond what we know and to hope that our cultural faux-pas don't land us in trouble. But much more than the fear of these things, is the ANTICIPATION of leaving behind those we love.
My friend asked me the other day, "why are we doing this?" .... I stared at her for a moment, trying to form an intelligent response. I recall the excitement we greeted this with originally, the challenge, the adventure, the experience we imagined we'd have. But that was not the answer she wanted, that was not the answer that would satisfy me either. There was no pat answer to her question. The discouraged tone she asked it in made me really wonder, why are we doing this? Why in the world do we want to pull a crazy scheme like this, waste all our savings and more, go far from... well... everything we know, make all our relatives question our sanity... I didn't know the answer. (And as anyone who knows me can attest to, I hate to give the wrong answer and will often remain silent if I can't give an answer I'm sure of.) And so, finally, I said the one thing I could, that wasn't really the answer I seek either: "We are going because this is the trip of a lifetime. We will be talking about this until our dying day. Our grandchildren will beg us to tell these stories, or stop telling them. We will never have an opportunity like this again." (okay, maybe not quite so formally put, but you get the drift... and sorry... but it's true, you'll probably be telling us to shut-up already about our travels within a few months of us getting back) So I gave her an answer, and it suits us well enough for the moment.
I just never imagined it would be quite so difficult emotionally to leave. I still have a month left before I go, and sometimes I wonder if I really want to go. I will go, I'm committed, but it makes me wonder how people manage to move thousands of miles away and do it permanently.