Hmmm.... Give me one that I've never read before
There is the myth that being a childhood friend automatically makes you lose.
But there are plenty of childhood friends that win.
The only factor that matters is if the childhood friend is the main girl or secondary girl or not.... but that literally applies to literally every single character that's in the hypothetical harem.
Meaning that being a childhood friend LITERALLY is not a factor in if a person would win or lose.
If the girl wasn't a main heroine, then she's guaranteed to lose, even if she was a childhood friend.
On the other hand, if the childhood friend is the heroine (or secondary), then it's possible for her to win....
So being a childhood friend is a complete non-factor....