Wild theorizing already. Good work, Elagune. Your fanbase likes this.

As to my theory, he picked fourteen because it's twice 7, one more than 13, same reason the dwarves recruited Bilbo, to avoid the unlucky number. Mainly because 7 was easy to remember, though, and once he had 7 things, he just devised opposites for them.

...Yup, planting wild theories, waiting for them to grow.