I used to tie ugly knots. Yup, being a mostly self-taught sewer and quilter, I didn't know there was a technique. I'd get myself in a tangle and it used to annoy me. I'd seen people tie knots fast and neatly but just didn't know there was a trick to it.
One day I got around to learning how. I can't remember who taught me, but my knots are neat and tidy and look like a little bit of magic when I do it fast. So thank you anonymous teacher!
I've taught a few people now too and it always makes my day when they get it. So I ventured into the realm of video tutorials and I've uploaded a knot-tying video to YouTube.