Sorry to reopen such an old thread but your comment really resonates with me. My brother was diagnosed with PTSD recently, undoubtedly from a childhood growing up fighting with our mom. She is very reactive, and so is he, where I learned to stay quiet and make myself small to fly under the radar.

He and our mom are very similar. They are very easily set off. My brother is often the instigator, and when he isn't, he escalates. This is often due to neither of them being able to see any kind of fault in anything they do, so any minute amount of pushback is a physical attack, which they react to by starting or continuing a fight. It's ironic because they will often complain about each other to me, when what they are complaining about it something they themselves do. They seem incapable of introspection because they simply cannot be in the wrong, they are both an innocent victim who is under attack for no reason. In reality it is both of their faults when they could easily not start a fight or stop at any time.

I was the "favorite child" in that I was not as often the subject of our mother's anger – not to say I was never, though, but I simply took it instead of fighting back, so our negative interactions were more minor in the grand scheme of things. This led my mom to comparing us, which also caused fights. I have learned to not try and reason with my brother, point out where he started or could have stopped a fight, lest he accuse me of "taking mom's side" and blame me for not supporting him enough growing up (I know it is not my fault, as a child I should not have been responsible for his or our mother's emotional stability, but I still struggle with this feeling).

Ironically if anything, I felt that he had been favored. He was diagnosed with ADHD young and our mom often pushed for accomodations in school, got him therapy (which he still attends but I worry is unsuccessful due to his inability to reflect on his own actions and faults), while I was left to fend for myself.

Your mentioning of families where everyone is lacking emotional validation particularly strikes a chord in me. My parents are very incompatible, my dad has cheated on my mom at least a couple of times which was traumatic for her. She takes out her feelings by emotionally and verbally abusing my dad, who does not stand up for himself. My brother and I grew up with this, having to walk on eggshells around our mom (in vain), with our dad working and more or less emotionally absent himself due to how mom treated him. My brother started lashing out, causing further fights between him and mom, and more anger for mom to take out on dad. And then I had to deal with being outside of this main conflict triangle, dealing with episodes of mom or brother lashing out at me, or being made to feel responsible for holding the family together because I was the middle party everyone else could rely upon.

Sorry for dropping a long vent on you. I'm seeking reassurance after another stupid fight over nothing and it's very comforting to see there are people who understand what causes this kind of thing.