Sing a song of pennies,
A pocket full of rye,
Lots and lots of blackbirds baked in a pie.
Lots of blind mice,
Lots of blind mice,
See how they run...
Yes, sir, yes, sir, several bags full
I wandered lonely as a cloud
That floats on high o'er seven hills
When all at once I saw a crowd
Of four and twenty daffodils.
Let us go through seven half-deserted streets
The muttering retreats...
Do you see what I'm getting at? Precise numbers sound folky. Of course, that isn't an iron rule, but it is a standard ingredient in that folksy flavour. Indeed, the best imitators of folk use this all the time. Coleridge's Rime of the Ancient Mariner is a classic example. It's almost an exercise in enumeration. He starts it off in the second line:
It is an ancient mariner
And he stoppeth one of three
Why three? There's no particular point to the number. And Coleridge does not stop there. There aren't just lots of people on the ship, there are:
Four times fifty living men
Who are condemned when a pale lady "whistles thrice." Things don't happen in weeks, they happen in:
Seven days, seven nights, I saw that curse,
And yet I could not die.
Like one that hath been seven days drowned
My body lay afloat;
The albatross accompanies the ship for precisely nine days, and the spirit follows the boat not "deep in the sea", as most poets would have put it, but exactly "nine fathoms deep".
The same trick is used by the great faker of folk songs, Bob Dylan. Here there are too many examples to name - seven sad forests, six wild horses, fifteen jugglers, five believers, fourth time around - once you start listening for them they're bloody everywhere.
So if you want to write something that sounds traditional and folky and magical - just chuck in some precise numbers. Simple.
Why this should be is a slightly odder question. And I have three different possible answers.
1) It reminds us of the Bible - the forty days and forty nights, the twelve disciples, the ten plagues, the four horsemen, the seven tongued angel etc etc etc. It could also, perhaps, remind us of magical spells in fairy stories where things often have to be repeated a particular number of times.
2) (And this is related) Numbers feel significant. When you read in the Ancient Mariner that the spirit was nine fathoms deep, you wonder what that means. It's as though there had been an ancient significance which is now lost in the fogs of time.
3) It's how folk actually talk. Poets and novelists will usually say that somebody stayed somewhere a long time. Actual people will say that they lived in Paris (or wherever) for three years. Nobody says "I work high in an office block." They say "I work on the eighteenth floor." Creation is vague. Life requires counting.
*Louis Armstrong lived before YouTube