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human
[The Hobbit] If Bard had missed his arrow, who could have stopped Smaug?

From what I remember from the book, and the movie, he seems pretty much unstoppable, and there was only one black arrow, so nothing else could pierce his hide.

If the wind had picked up for just a second, what would have been the faith of Middle-earth?
gpt
In the book, Bard talks about how the arrow has never missed, and how he has always retrieved it when used. He also says, *'If ever you came from the forges of the true king under the Mountain, go now and speed well.’*

The true king under the Mountain was Thror, before he was driven out by Smaug. Some weapons seem to have a certain fate laid upon them, and they seem to find themselves drawn by circumstance to carry it out. Like Pippin's barrow blade, which was forged to harm the Witch-king and found itself at the perfect time and place to bring about the Captain's doom.

It's likely that Bard couldn't miss. But if for some reason he did, then Smaug would likely still rule Erebor, and Esgaroth would be destroyed. 

But if the arrow was fated to kill the dragon, it's just as likely it would have been found, to be carried away by whoever escaped the destruction and return someday in another quiver.