When a story is the only thing keeping one from being essentially killed by monsters that prowl the forest surrounding the castle, what would one do? One would tell a tale.
And if there is a pledge that the best story will get a reward, a reward of untold fortune, what would one do. One would tell a better tale.
And then there is a vow that promises a plight of unimaginable misery, to the one with the worst story. One will hope not to be the one.