I find it helps to ride out the rough patches by remembering that we set ourselves on this lifetime's path before we got here.
I also subscribe to the 'there are elements of freewill in amongst our destiny' philosophy. Some parts of our life are set in stone, while the paths in between getting from stone to stone are what is left to free will.
I also believe we will never have access to the full picture while we are here (that would blow our tiny brains, lol) but we do once we are back up there.
I agree it is really tough to keep the faith when you're going through the really, really rocky stuff - and of course those are the times you need it the most. And hey, if a lesson wasn't tough, we wouldn't take so much notice of it would we?
We are all in that ever-upward spiral to re-enlightenment, I think. :)