People make them happen. First, strong families are committed to making the family work. Such families don't expect perfection from each other. They accept each other as they are, and accept responsibilities and work together as a team. Their commitment goes far beyond feelings.
Feelings are important and are integrated, but they come and go.
They are variable. Commitment is constant. It is an act of the will. In other words, if we want a strong, happy family, we need to be committed to making it happen. Second, happy families spend time together, not only quality time but quantity time.