Reason and faith both are your faculties, but on any given issue they are almost mutually exclusive.
I disagree. Depending on what you are doing/thinking you would use various levels of each.
Would you please tell me why do you prefer faith over your own reasoning abilities on any given issue including the unseen?
We don't know everything. In fact, we can't know everything. In order to move forward on certain issues we need to have a leap of faith that what we think about a certain point inside of that issue is true. There are certain things we deal with, like mathematics, that require pretty much total reasoning/logic and little faith. Others, like the Unseen, require mostly faith.
Such is the the case with all of the various tools in the human repertoire. You don't use everything for everything.