It is said that in JRRT's original ideas for the story, Bilbo somehow ends up killing the dragon. This might sound implausible given how small a hobbit is compared to a dragon, but really the ratio is not so different from that between a man and a dragon. It does, however, make for a very different story. Bilbo had a role in Smaug's demise, both intentional (spying his weak spot) and unintentional (talking about it in front of the thrush, and then sending Smaug on his way to attack Laketown), but it is Bard who is the grim, dour, pessimistic, doom-predicting warrior that is able to shoot an arrow into Smaug (point, shaft, feather, and all).
One gets the impression, given his introduction as the guy who is always predicting bad things, that Bard had in some sense been preparing for this moment all his life. Perhaps growing up as the descendant of leadership of a town that was obliterated by a dragon, makes you think about bad things happening more than other people do. Regardless, he has obviously been practicing his archery, and also knows something about how to prepare for combat and keep your head during the battle. Just prior to the thrush showing up to give him some timely advice, Bard had as far as he was aware no reason to expect his last arrow to do any more damage than the hundreds of others that the town's archers had shot at the dragon. Yet, he was not leaving until he had shot his full quiver.
One recurrent theme in JRRT's writing, in both the Hobbit and LotR, is that he not only describes the battle, he describes the aftermath, and it is not all joy and celebration. In fact, for the most part, it is dreary and full of grieving. The people of Laketown are, we told, not only sadly diminished in number, but will go on to lose more in the winter to come. Yikes.
The Master of Laketown is, of course, despicable, and pretty much does nothing useful the entire chapter.
Chapter 15