Who you gonna call?

I continue to be woefully ignorant to how the media can call a state for a candidate when 0% of that state's voting precincts have reported results, and they used an exit poll of, what, a few hundred people to determine who will win? Seriously, especially when what has been reported shows one candidate ahead by double digit percentage points but it's called for the other guy...I guess the race to be "first" wins out over things like reason, and ya know, patience. :x