An assumption is a shortcut through a neighborhood you’ve never actually walked.

You fill gaps automatically, and the filling feels like knowledge because it arrives in the same voice as knowing. Most of the time the shortcut is fine and saves you effort. The trouble is that you cannot tell from the inside which gaps you filled and which you actually walked, so the guesses and the facts sit together looking identical.

Pick one belief you act on regularly and ask where it came from. Did you see it, were you told, or did you assemble it from two things that happened to sit near each other? Checking one a week is enough to keep you honest.