For me, knitting is a stress buster. I knit to keep myself sane. It's a procrastination technique, but it's also soothing. The repetitive motion of stitch after stitch, row after row, one needle to the other, lets me think. With a simple pattern, my mind can sort itself out. I think in song lyrics, or about my day, or about any amount of work I have to do, or planning for a zombie apocalypse. When I have a more complicated pattern, I can't help but concentrate on it, and my worries sink for a little bit. It's lovely. As an added plus, I get cozy warm and hopefully awesome items out of the deal.
I think everyone should learn to knit, for all of the above reasons (except the robbing banks one). Yarn bombing can free the artist in you, as well as the rebel and that inner ninja. Knitting for others unlocks compassion, as well as an appreciation for the work and love that go into making something unique and custom. And knitting for yourself is the ultimate win-win situation: wearable items, and distraction. Perfect!