Well IN MY OPINION, I understand the book was being told in an African American female's perspective, but I'm sure that many people of various races feel this "shift" as well.
I'm non-white living in California. I'm sure everyone believes that we are a multi-cultural State where being "accepted" for who you are is easier than anywhere else in the U.S., but I definitely find myself switching my speech/demeanor around various environments. I believe that for anyone to succeed you have to make that SHIFT, its instinct. I don't feel like its a form of "selling out."
I've gone above and beyond the norms of where statistics placed me. I came from a home where both my parents came from another country, I grew up in the inner-city, and my family income was at California's average poverty level. But what my mother instilled in myself and my siblings was to GET EDUCATED. Went to college, got my B.S. in Business and am where I am today. ( A peon in a construction office, lol)
In school we are taught "proper" English and Grammer, and the teachers/professors spoke to us in a professional manner as well. You gradually learn that in order to interact on a level outside of your norm, you have to be a chameleon and adjust...or communication is often blurred or lost.
I cannot imagine coming to work telling my boss "yo watz good son!" or referring to my co-workers as "homies" but those are words I use outside of the office when I'm at home...and I doubt that the sweat pants I rock at home would appease the "business casual" rule either. Different situations call for different methods, today's society tells us to "shift" in order to fulfill these various situations in our life.
This is a very good topic, and despite the fact that I am not African American...my daughter is half, and I want her to be fully aware of the obstacles she may/may not have to face. All I can tell her is the same thing my mom told me...GET EDUCATED, and make a better life for herself. If she feels that she has to put on two faces to get ahead then that is a choice she'll have to make for herself.

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One smile from her & my troubles melt away!