Why does sed require 3 backslashes for a regular backslash?

Question

I\'m curious, why does sed need 3 \\ just to recognize one? I\'d understand it needing 2, but 3 I don\'t.

EDIT: here\'s an example on my Windows compute

Answer 1

Replacing one backslash with two on my Cygwin requires this expression:

sed -e "s|\\|\\\\|g"