I work in telecommunication and see fiber quite regularly.

It really is thin, and fine is a better word. In general what you see is the coating of the fiber, and that already is very fine. The fiber itself is nearly invisible even when you hold a strand between your fingers against the light.

A single of these nearly invisible fibers can transport a GBit/s into your home. “Any sufficiently advanced technology is indistinguishable from magic” - yep, Arthur C. Clarke was right.