Critique and Advice; the treadmill of adventuring.

I've had this idea for a story fermenting in my head for over a year now, and I really want to write it as a forum adventure. I've got all the characters I want to use, the setting, the theme/feel of the story, the beginning, end, even the middle, all fleshed out. But I just can't connect it into a plot?

Somehow I just can't figure out the goals and motivation of the main character. I know why he got himself into this situation, but I don't know how he's going to get himself out, or why he does what he'll do afterwards. Not only does this lack of motivation make it really hard to have a cohesive plot, having a clear goal to work towards every update is one of the most important parts of a forum adventure. The lack of a clear goal/way to measure progress is what made this adventure fail the first time I ran it.


Does anybody have any advice? Is this something that you can give advice about, without knowing more of the story?

edit: Actually, I think I might just put this one on the shelf for a bit. In the time since I first thought of it, it's only grown more formidable, and my need to make it perfect has only grown worse. I'll probably save it for a time when I'm more equipped to handle it/possibly completely rewrite it.

edit nullified due to fogel's sage wisdom