Lynn,
Although I spent 3 years as a personal trainer, my time spent training for long-distance running was not inspired by my profession, but rather by what I was going to have to do in order to accomplish it.
Although I was in good shape, I had smoked during most of my adult life, and I had always hated running.
I knew that by training for the event (a half marathon), that I would have to train harder and more consistently than I ever had before, and that my level of health would soar as a result.
As it turns out, the race that I was going to do with a few friends never ended up happening, but by that point I was already in love with
the benefits that I was going to get from the training, so I kept at it.
I ran 13.2 miles twice, and I wasn't even registered for an event. I just wanted the benefits and to be able to say that I did it.
So, my official advice is to ask yourself
why you want to do it. If your "why reason" is strong enough, it will keep you on track for the long haul.