I've not observed any common link. Duality seems more of an exception than a rule because cognitive needs are overshadowed by animalistic desires. Far more dual pairs exist in work situations where they're thrown together by circumstance but none that I've known ever became intimate because they had some serious gravity between them - au contraire. Most dual pairs that I've met outside of work seem to have gotten together later in life and stayed together simply because over time and in hindsight, they realized that they felt comfortable and safe with one another. Duality seems to sneak up on most pairs; it rarely hits them in the face; and despite the duality factor, a majority of people still choose to go their separate ways because there are so many other issues.

a.k.a. I/O