The trick would seem to be trying to get the best of both worlds. In many cases the game (in this case the temptation to slack off and let yourself go) is played unconsciously. Commitment and trust, however, tend to be higher level features. The best lovers are, by hypothesis, able to foster security and trust while at the same time keeping competitive instincts in play. The impulse to satisfy all the partner's desires before they stray. The spark.