Facepalm

Yup. It's always good to keep in mind that some issues are hidden and that your perception of someone is different to who they truly are, as OP said. But there's no Universal Law of Conservation of Personal Problems that dictates that everyone must have the same level of significant problems in their life. Some people have less, and some have more. It usually averages out but there will be people on either end of the spectrum having a very bad or good time.