Establishing your own boundaries is part of a whole. The other part is respecting other people's boundaries. What goes on inside other people's boundaries is their business. If they don't share some part of their life with you, don't ask about it. 1. Share your own experience.
Coercion is one of many ways of stepping on others' boundaries.
Ask without intruding. Admit to a lack of knowledge or understanding. Remember that it's not your responsibility to understand why someone else does the things they do. Remember that irrationality is often in the eye of the beholder. We are only responsible for our own lives, and no one else is responsible for anything in our lives.