My last yarn fail happened when I found a scarf pattern in a crochet magazine that I thought would suit a friend of mine, so I dug out a lovely variegated yarn with a light sheen out of stash and started it... only to run out of yarn about 2/3 of the way through.
The design consists of triangles - I was supposed to end up with 16 and I only had 10. Attempts to match the yarn failed, as not only did I buy it four years ago, so the store no longer stocked it, but I'd lost the wrapper of the skein so didn't know brand or anything. I could have left it as a short scarf, but that seemed terribly poor form for something that was going to be a present. Annoyed with myself, I gave myself a stern lecture on how I should plan projects more carefully. Weeks later, I went and bought some new yarn, still variagated but with a stronger colour palette, to use for the scarf, and I started again. The unfinished scarf got shoved into a small bag and left under my craft desk.
Today when I was clearing up said desk, I came across it and thought that there had to be something I could do. In line with the interest in ethical fashion and moving towards more ethical crafting, I couldn't just throw it out and waste the yarn and my time, but I didn't want to unravel it all either.