The idea of comparing a human to an onion comes from the similarity between an onion's many layers and a human's many layers. Everyone has different layers of their personality, their life, their experiences (etc.) that they don't publicize to people, whether it's for the fact that they don't want to or they just don't have the opportunity to. Personally, I think that people can have different things within their layers; not everyone has experiences behind their emotions and personality, but some people do have experiences that change their life. I think that this goes along hand in hand with stereotyping because most the time, your top layer (or two) is all that everyone sees, so people judging you based on these few characteristics that you have or mannerisms that you do isn't really accurate just like stereotyping people based off their race or religion because, once again, that's just one aspect of your huge life.
For me, my many layers include the emotions and experiences behind those emotions. Experiences have a way of completely turning your world upside down sometimes, which has helped me becoming a bigger, better person than I was before those experiences. My many layers contain the emotions, love, and relationship that I have with my family, the love that I have for my close friends, and the respect I have for my elders. My layers contain the nerves along with the excitement of graduating undergrad college and moving onto law school, then moving on to the real world, as my dad likes to call it. My layers contain the things that make me, me. Some of these layers, the public can see, like how I am blonde and short, or that I like to enjoy myself 100 percent sober to the point where people, including my friends, think I've snuck a few shots behind their back. But behind those layers are experiences and emotions some people can't even fathom, but I love them because they are what makes me who I am.
Now let me ask you, what are your layers?