Wisdom. Life gets hard every now and then, this is what keeps the relationship from sinking. Having the capacity to lighten up each other's life and reminding each other 'why' you're together. Work hard, play hard.
You gotta marry someone who you know you'd still be down to fuck in the laundry room real quick while the kids are downstairs watching Lion King & 10 minutes left til the dinosaur nuggets are ready to come out the oven.