incompatible partner
It's hard to be your own quality control. It's hard to make sure you behave as well as you can, if all you have in your checking toolbox is the same sort of thinking that made you do the thing you just did. It's hard to improve if you constantly believe you did the best you could in each situation.
Sure, we all do the best we can in each situation, given what they knew at the time, their skills and abilities, the resources available, and the situation at hand. But surely, if we knew what we know now, we would've behaved differently in many situations. Or would we? I pose that we oftentimes wouldn't. We oftentimes behave worse than we know we could, knowingly, or at the very least we let things through and ignore that we did. An acidic comment to our partners, a rabbit hole or a moment as Karen when we could've been polite.
What's the antidote to this? Well, I can totally see two Karens ganging up on a poor waitress regarding a bill. Group think. So just adding other brains into the mix doesn't seem to help us check ourselves.
We need a different perspective. It'll be painful, oftentimes, but it will allow us to grow. It'll allow us to know, just that little bit more, that our perspectives have been checked from two sides. It'll allow us to see things with different eyes.
Now how do you achieve this? It's simple. Choose a partner who is more unlike you than like you. Choose a partner who likes to talk things through. Choose a partner where you do have differences in fundamental values.