Complex sentence: The inclination toward working toward one's own advantage and also the inclination toward fairness must find an equilibrium within the relationship, and the second inclination tends to come out on top as partners strive to get what they deserve, no more or less.
Split into simpler sentences: The inclination toward working toward one's own advantage and also the inclination toward fairness must find an equilibrium within the relationship. The second inclination tends to come out on top as partners strive to get what they deserve, no more or less.