[Olorin]

I remember reading a study that dealt with the relative taboo. It basically found that when you grew up with your siblings and cousins, you were not romantically attracted to them. On the other hand, if you met a relative, like a cousin, after you were adults, then attraction was possible.

For those adults who found themselves attracted to their cousins, they still generally did not act on it, due to the societal taboo, but it was a conscious restraint, whereas for cousins that they grew up with, they never developed romantic attraction in the first place (a subconscious restraint).