Everything we observe, everything we hear, everything we taste, touch, smell, experience is filtered through a lifetime of phenomena and exotica, things which combine to create the individual human. That is to say, each of us. So, too, your story people and particularly your point of view narrator or narrative voice. Just as we are all unique, so should our story people be unique. His emotional baggage.
Fiction differs first and foremost from other forms because it is about emotion.
Emotion imbues every reaction we can hope to have. Often it works on so subtle a level as to be invisible. Every single line of dialogue should not be weighted with heavy emotional power. Nor should every paragraph of description. But much of it should be because that makes our fiction more dramatic.