It is an aspect of all relationships. It develops slowly and is not noticeable initially. It becomes noticeable only when the gulf is much broader.
Some people visibly never cry, while other people show no perceptible emotions when watching a tear-jerking show or when in the middle of an emotional situation.
The fight or flight response comes to the fore. People tend to become aggressive or run away. Or they may create walls around their ego, in order to protect themselves.