I read "Crucial Conversations" around the time I turned 35 and it changed how I manage conflict in my relationships. These days I always first try and understand why someone is upset (pro-tip: it's frequently not what they lead with).
> You can't win an argument. You can't because if you lose it, you lose it; and if you win it, you lose it
I also love this more general one from Marcus Aurelius' Meditations:
> A cucumber is bitter. Throw it away. There are briars in the road. Turn aside from them. This is enough. Do not add, "And why were such things made in the world?"
Seek first to understand, then to be understood.
aka “Seek to understand before seeking to be understood”. I’m an atheist who happens to find great value in the St. Francis Prayer.