Why acupuncture seems to work

Chinese Acupuncture Affects Brain's Ability To Regulate Pain, UM Study Shows

I find it remarkable that sticking fine needles into skin seems to genuinely help with various aches and pains. This study suggests the brain mechanism behind it, but I guess it still doesn't explain why the fine needles (which you can barely feel, from the one time I had some in me) in skin cause that reaction in the brain. (To be more specific, maybe it's not surprising they cause some reaction in the brain, but that it should be big enough to have effect of other aches and pain still seems very odd to me.)