Marriage: Together for shared interests, apart when that balance breaks

Children — shared children are the common interest between spouses.

In raising them together, you invest countless hours and energy. This is your shared sunk cost — and also the cost of tearing you apart.

Marrying is building a shared interest; sustaining a marriage is sustaining that shared interest.
The more common interests you have, the higher the cost of dissolution; the fewer, the more fragile the bond.