I would say it is a skill which has its downsides. It's not about assumptions, not about thoughts or knowledge in the superficial sense but about body language and what is unspoken, not spoken. To be able to read another person you observe their body reactions to their environment. Their gestures, face expression and the like tell you what they really feel.

After all, when you are a child, the adults say something with their mouths but that is not important, for what they speak, often does not reflect what they do.