If the feelings are warm, a husband and wife can enjoy one another's company, overlook a partner's troubling or annoying traits, communicate adequately, and still express affection.
But when the feelings cool, one or both find they have no reserves or capability to love an obviously imperfect person. Now needs are not met, which causes hurt, which promotes defensiveness, which reduces positive communication, which heightens misunderstanding, which provokes conflict, which fuels anger and bitterness. If forgiveness and reconciliation do not break this downward spiral, the ability to love one another is paralyzed.
This pattern in nearly all relationships may be avoided for awhile as long as the tough issues that provoke selfishness do not exist or are obscured. But sooner or later reality hits. In spite of a couple's best intentions, they eventually realize that two independent people cannot both have all of their needs met all of the time.