All of those circles is a person. Each circle is a role that a person plays in his life. Or you can call it a layer of skin or a mask he wears. Those layers are built to protect some vulnerabilities, to cover some imperfections. Some are created after some significant events in the person's life. The events can be good and can be bad. That's why the circles have different colors. To get to the inner layers, you need to have similar experiences, to share the same kind of events in your life(figures on middle left). Besides those you need to know when and how to approach, so the opening and the key would be aligned.