The idea that a relationship between two people is a 50-50 proposition seems both obvious and fair. If both people pull their fair share, the partnership will stay balanced and healthy, right? It seems only logical that to achieve a fulfilling relationship both parties must uphold their half of the bargain. But relationships are too important to "meet in the middle".
When I am counseling a couple to improve some troubling aspect of their life together, sometimes it is very easy to determine who owns most of the responsibility for change. For example, if one person has an affair it's not appropriate to say that his or her partner is somehow "to blame" for the infidelity. There are better ways than infidelity to handle dissatisfaction.