Could it be that the same sorts of excitement, when experienced time and again, are no longer experienced as excitement? Does the skydiver with 100 jumps behind him or her feel the same rush of adrenaline or awareness when poised at the door as they might have when braced for their first couple of jumps?
How about you? Does your pulse quicken like it did when you confront what is now a familiar situation that you might have initially thought dire or dangerous?