What makes every human different?

My sister always behaves completely differently than me. I am always shocked at why she behaves differently. We have both been staying together since she was born. Mostly, whatever I eat and drink is the same as hers, and we even studied in the same school. But I discovered many differences between myself and her. when I met one of the twins' sisters. I am curious and want to ask some questions about this. Are they the same? Are they the same in all circumstances? I got an answer of no. Why do people change their behavior? Why do people change over a period of time? Why do relationships change over a period of time? I had always listened that she/he changed now. 

I found all these answers in the book of peter bevelin seeking wisdom: From Darwin to Munger, 

       The brain changes continually as a result of our experiences. Experiences produce physical changes in the brain either through new neural connections or through the generation of new neurons. Studies suggest tht the brain can change even during the course of a day. This means that the anatomy of the brain varies from individual to individual. Even identical twins with identical genes don't have identical brains. They have had different life experiences. Experiences are the reason that all individuals are unique. There are no individuals with exactly the same upbringing, nutrition, education, social stamping, physical, social and cultural setting. This creates different convictions, habits, values, and characters. People behave differently because differences in their environment cause different life experiences. This is why it is sometimes hard to understand other people's behavior. To do that, we must adapt to their environment and share their experiences. This is often impossible.

       If we encounter a stressful situation, how we respond depends on what we were born with, what we have experienced, and the specific situation. Assume that a person "Sam" and you both have genes for "being fearful." You are standing in a Savannah in Africa and are approached by a lion. Do both of you show the same reaction when exposed to the same situation? You are afraid but not Sam. Sam either knows that this lion is tame or Sam is a lion tamer. Sam's reaction comes from his life experiences. Sam may also be genetically predisposed to react differently to certain dangers. But even if Sam has a low genetic vulnerability to fear, he can develop a fear of the lion. One horrifying experience with a lion may be enough.

    Overall, we need to be humble with each other because we do not know what type of upbringing happened to them. Try not to judge someone based on their behaviour.