Case. They married at 63 and 67. Six months later — deadlock: each has a home, money, grown children with opinions, and neither wants to “move into someone else’s life”.
Model. Two mature autonomous systems merge with no room for long grinding-in: refactoring habits at this age is costly; integration works only through explicit interfaces — agreements.
What helped. They stopped expecting a youth-style merge: kept both apartments but started a shared calendar, a joint budget for joint things, and the rule “children advise, they do not decide”.
Lesson. A late marriage rests not on grinding-in but on respect for what is already built. Do not merge the systems — bridge them.