LOL I didn't know you followed this 'rule' as an old wives tale, Cara. Do you suppose that it is really a way the older generations have been able to manipulate what the culture at the time respected: i.e. no work on Sunday-it's the Lord's Day?
I think much of the old wives tales were a result of people not understanding the laws of nature and through ignorance devising ways to 'control' their environment.
I also believe that some of this was out of the cultures mores and again, a way to get people to follow the 'tradition' of their society.
One old wives tale I heard from a h.s. g.f. was it was bad luck to wear shoes in the house. Well, from a housewives perspective it would create more work. Woe be it to the person that would do such a thing. Therefore, in reality it was 'bad luck' for that person to cross that line of consideration trampling in through a clean house after being out in the farm or woods...or even the dusty streets.