Human beings are highly adapatable creatures, but what that means is that we are deeply affected by our environment, whether we like it, or in fact even realize it, or not.
The way you spend your time defines you. No, not just that few hours per week or month that you may find to do the things your "true" self might want to spend time doing, but all of it. The third of your life you spend at work defines you. The time you spend in traffic. The time at the grocery store.
The people you choose to surround yourself with define you. Have you ever started spending a lot of time with someone, then noticed that you picked up some of their phrases and gestures?
The things you own define you. As much as you may want to believe you are not materialistic, the truth is the things we own become an extension of ourselves. The clothes we wear, the tools we use, these become an intergal part of the way we experience the world.
How you look defines you. It is a simple fact that people are treated differently based on how they look, and people respond to the way they are treated.
You will become your environment. So choose it well.