When couples are emotionally close, Tesser found they automatically and unconsciously stake out complementary domains. It is almost as though, recognizing the potential threat that competitiveness poses to an intimate relationship, the unconscious brain nudges people toward complementarity.
Tesser found that if one partner has a strong preference to do task A over task B, but the other partner has an even stronger preference for task A, the first person unconsciously switches preferences and says he actually prefers task B.
That's from Shankar Vedantam's The Hidden Brain.
