most often, in one form or another is that it's scary. change means that the way things are now will not be this way any longer and they will be something different. it's impossible to know what this new state of things will be like. will it be better? worse? no one can actually answer that. it can be tempting to try to keep things the same since there is comfort in the expected.
however, i think it's helpful to challenge this idea. no matter how hard you try to keep things the same, they will not stay that way. the world is constantly changing; look at how day turns into 