If you're anything like me (and let's face it, you are, whether you like it or not), you'll enjoy telling a good story with an amusing denouement. That's French for punchline. You'll also be aware of the intense frustration that arises when someone butts in before the end and delivers the puchline for you, wrecking the delicate timing/set-up you'd mentally worked so hard to achieve. My point is that a good story is easy to wreck.
(Cheers to Dr. Snafu for the pic, brilliantly entitled "Why the long face?")