One night this senseless rule came out of a smelly person's reflections on life.
At the other side of the planet, a "zealous and spiritual" , well meaning sister will meet a brother who doesn't fit this temporary-only-apply-it-to-others criteria. She will ditch him, convinced that she's doing the right thing.
She'll go marry somebody who'll be a mismatch to her, but she'll see him as okay because he falls under this 'good brother' category.
She'll end up regretting her decision when she'll see that people who invented this rule are letting their own kids marry whoever they want.
And life will go on in jw world with bitterness...
T in a T