Human Nature and Procrastination

What is it about human nature that allows us to put so much enthusiasm into one thing while making an equally intense project feel like just so much of a chore? 

When I have baby gifts to knit or crochet, it never seems to be too much trouble to pick up the needles or hook and spend hours working and praying over the project. When my mom wanted a new sweater vest, and we settled on a project with cables running up the front and back, I was engrossed in the growing design. It made me so happy just to work on it. I thought nothing of spending eight or more hours a day with the needles in my hands. Not only was I happy to do it, I felt blessed by the process.

I've been working on a short sleeved sweater for myself for over a month now. I'm slowing down. The back is done, along with one front side and a third of the other. It's really great yarn, turquoise and very soft, so it feels good on the fingers. I can't use the scratchy yarn excuse.

It's the first sweater I've made for myself since high school. I graduated over forty years ago. I keep myself pretty busy with gifts, so it's not like it's been intentional. I've just been very surprised that I can't get the excitement and energy and joy out of the making as I get when I'm working on something for somebody else.

Human nature? Just what's natural about that?