"Monogamy becomes boring when couples become lazy"
Whether we want to admit it or not most of us look forward to getting to a place or time where we can "relax" and "take things for granted".
We can’t wait for the “probation period” to end at a new job. There is an element of stress that comes with trying to hold onto something. We look forward to a time where we don’t have to put in our best efforts to “maintain our position”. Some people see this as the time where you don't have to "worry" about what you "say" or how you "act" because their mate is not going anywhere. In their mind "love and commitment" means "forever" regardless of what happens.
In reality there is no such place or time! Marriage like a job is an "at will" contract. (Being in a committed relationship does not mean you can stop being good to your mate and they won't go anywhere.)
No one is "stuck" with anyone. You have to keep "impressing" someone to keep them. Competition never really goes away. A garden must be nurtured to remain alive.