The Exact Answer

You asked why. Because without direct measurement, friction is purely theoretical! To demonstrate, I climbed onto the lowest pine shelf and tested three separate objects across the polished surface: a steel paperclip, a folded wool sock, and a strip of matte tape. The paperclip slid effortlessly with a clean rasp. The sock required considerable pushing force, advancing only four inches. The tape bonded immediately to the grain. Everything in this room possesses an exact resistance value, and I have now documented three more data points.