It's pretty fascinating to watch little kids and the various ways they respond to change. It is always the idea of change that is the hardest, rather than the actual change (though this can be difficult as well). I was one of those completely (and inexplicably) anxious kids that suffered a lot of fear over change. According to my parents I grew terrified when even the doorbell rang as it signaled a change in the family's routine. I did not like to go places, meet new people, even our family getting a new car made me uneasy. On the other hand my sister thrived on new situations. I have two sons. My older son was shy but extremely confident. He welcomed change and still does today as a young man. My younger son was more like I had been as a very young child, terrified of change, but outwardly less shy than his brother. When I look for commonality in our natures I can see that both my sister and my older son are less emotional people than my younger son and myself--perhaps this knowledge that you will experience new emotions (the most uncontrollable aspect of being human) might have something to do with the level of fear?
Because I was who I was as a child, I began a lifelong battle against my own fear and anxiety starting when I was about 13. I have made it my mission to confront and try to understand the workings of this aspect of my nature. What I have found is that I will always carry a certain amount of fear when it comes to change but that I can push through it. It is incredible to what extent humans sometimes prefer the familiar (no matter how painful) to the unknown (people in abusive relationships, longtime prisoners etc). Rationally I am able to see this and to want to change this in myself but emotionally I still carry fear.
My mother is someone that does not seem to possess one iota of fear about the unknown and she is also affectionately dubbed the queen of denial in our family. Do these two things relate? I think so. When I am faced with the unknown, my imagination serves up the worst possible outcomes first and then I reel myself back in. My mother on the other hand would immediately imagine the best possible outcome. (When she had a very aggressive cancer 11 years ago she was given 20% odds of survival, 80% not surviving. I was devastated but she said, "Why would I assume I will not be in the 20%? Someone has to be in that group!")
Last thought: pushing the envelope around one's own "comfort zone" may be the scariest thing a person can do but don't you find that it is also the most profoundly rewarding?