The concept of a shadow child is very interesting. It's the reason behind any of your own actions which you would consider an overreaction.
It's basically the remnants of a childhood traumatic event(s). Some people also have the inverse. Their shadow child decided the emotions were too much and decided wear a suit of armor. This can involve thoughts such as:
My feelings don't matter and will just worsen the situation.
Arguments are won with facts (*or emotional manipulation).
Emotions are a weakness.
There's no point in being sad.
Why am I not sad?