Of course the irony embedded there is that people, married or not, often change over time on their own, for better or worse, as they deal with the challenges of new situations or the sameness of old ones.
But if people married or in a committed relationship can't make each other change, I believe that they can train each other. In fact, I believe that successful mutual training is a necessary element (among others, of course) for a successful long-term committed relationship.
Training within such a relationship involves each partner learning:
1. how the other expects, or will tolerate, being treated;
2. what pleases and displeases the other, and whether it matters;
3. to accept and/or accommodate the other's ways;
4. to speak and behave in such a way that makes getting along possible;
5. when to apologize and whether or not one can get away with never doing it;
6. to forgive, or whether one can get away with never doing it.
I once asked a man from my church who was married for over fifty years what advice he could give on having a long marriage. He replied: "Well, I just learned that the kinder I treat her, the kinder she treats me. And the kinder she treats me, the kinder I feel like treating her."
And I thought, Ah, there's a couple who've trained each other well.
On the other hand, I know or have known other couples who've been married for many years, one of whom treats the other, or who both treat each other, with far less care than the man from my church advises. I expect those couples trained each other just as well, but differently.
Still, if I might evoke my pie crust analogy from a couple of blogs ago: people who are handled roughly become tougher and weaker at the same time; less resilient, more crumbly.
Not that even the nicest-to-each-other couples are composed of two perfect human beings; there's none among us whose bad bottled-up genie doesn't once in a while make an escape. We all make mistakes, say a wrong or hurtful word to each other, indulge in some inauspicious behavior; that's what it is to to be human. And that's when it's time to pull out training numbers 5 and 6.