Here's one more article that shows how knitting and doing other fiber arts reduces stress. I like this quote:
"Textile handcraft making was associated with the greatest mood repair, increases in positive, decreases in negative mood," she tells KNAU. "People who were given the task to make something actually had less of an inflammatory response in the face of a ‘stressor’."
I think there is something about "creating" that brings joy. There is not only satisfaction, but a deeper happiness that comes with making something that wasn't there before.
I once read Orson Scott Card's Alvin Maker series, and that was a theme in the books that I appreciated. Whenever they wanted to drive away the enemy, the simplest act of creation would work.