As you can see, the graph has two axes that represent knitting pleasure and
knitterly frustration, respectively. The z-axis is a combination of these two quantities. Knitting pleasure is a combination of variables, including how nice the yarn is, how much fun is the stitch pattern and how cool is the finished item.
Knitterly frustration is also a combination of variables, including mistakes in the pattern, annoying yarn and boring knitting. The exact equation for me is z=2x/y because I'm usually just happy to be knitting and can often overlook the frustrations.
I put a number of recently completed projects on the graph to demonstrate some of the above ideas. For example, the Clapotis was almost the perfect project. I loved the yarn, the stitch pattern and I wear the finished item all the time. My vest from Jaeger was really fun to knit and I wear it a lot, but the yarn was only OK, so it falls a little short on knitting pleasure. The Jaywalkers were made with great yarn and fit really well, but the stitch pattern got a bit boring and they took forever to finish. Finally, knitterly frustration is so high with Reynolds Gypsy (it splits like a mofo!) that no amount of knitting pleasure can overcome it and any project registers low on the knitting happiness scale.
These are just my opinions and I'm sure that the equation for knitting happiness is different for every knitter. Stay tuned for some knitting happiness from me later this week!