A person like anything else goes through several changes in life physically, mentally and emotionally. We may react to different situations differently at different times. The personality and character of a person does not change but remains the same although he may not be showing and adhering to it at times and the bottom line is that a person remains the same. We should not judge a person or conclude the personality based on what we see at a given time. It is possible that a person if put in to a character or role and act totally different from what we expect out of his personality. But that does not necessarily means he is changed. Just like human body parts can grow and form shapes to certain extent for certain period of time and then they only go through minor changes over the course of life, the same is true about personality. Some people when they get a dry skin, uses moisturizers to keep it soft and shiny while other just don't care about it and end up with really dry skin or even worst, their skin looks dead. Know a person with skin, condition of the skin could change but the person is still the same. Life is too short to know each and every one around us completely and very well. So those you know very well already, you have actually invested your valuable time on them. Don't loose them easily.