I have been studying knots for a little bit. I don't really know why. My guess is that it sort of tickles this spot of "things that I think people should know" Anyway, here's one of my favorites: the sheet bend. https://knotspedia.com/sheet-bend/ It can be used to tie two lines of the same or differing sizes together. It has been found on neolithic tools, and has nautical origins. If the eye of a sail has been torn out, you can fold the corner of the sail and tie the sheet bend knot to that corner.