In the amazing classic WWI movie, The African Queen, Humphrey Bogart portrays a coarse, drunkard boat captain, Charlie Allnut, who is hired by the straight-laced missionary woman, Rose, played by Katherine Hepburn, to escort her down the river in the African Congo. The two are very mismatched and Rose verbally objects to Charlie's drinking. Charlie awakens with a hangover after a night of indulging to find Rose pouring his bottles of gin into the river. He complains, "What ya being so mean for, Miss? A man takes a drop too much once in a while. It's only human nature." Rose replies, "Nature, Mr. Allnut, is what we are put in this world to rise above."
Many of our behavioral responses can be considered "human nature." For example, it is natural for people to blame others for their pain and anger. It is also natural for us to react defensively when feeling attacked. It is normal and natural to take things and people for granted over time. And it is natural for people to overlook all the positive characteristics of another and hyper-focus on their irritating traits. It is very natural and seemingly automatic to respond emotionally when in conflict with another person. However, as am quick to point out frequently in my office, just because it's natural doesn't mean it's healthy.
When faced with any kind of conflict, part of our brain is activated that has evolved for the purpose self-protection.