What is illusion of transparency?

Illusion of transparency is a concept in personal epistemology: People cannot respect boundaries they do not know exist.

Example: You resent your colleague for calling you at 9 PM about non-urgent issues. You have never told them you don't take work calls after 7 PM. In your head, this boundary is obvious — you have a family, evenings are sacred, everyone should know this. But they don't know. They call because nothing in your shared reality has marked that time as off-limits. Your resentment is real, but it is aimed at someone who violated a rule they were never given.

This concept is part of Phase 33 (Boundary Setting) in the How to Think curriculum, which builds the epistemic infrastructure for boundary setting.