As Living Proof described, I am a thinker and an "over" thinker. Interestingly, some of my best thinking is when I'm not thinking about it. A solution to a problem just seems to pop into my head; I guess my brain has been thinking about whatever without me directing the thinking.
Anyway, for me the "smile" is often AFTER the thinking/concentrating. The Fairfax County Cross County bike trail has a section that crosses a little stream, about 80 feet across of water 6-10" deep. First time Lynn didn't make it across, but I did. That brought a HUGE smile to my face. Riding through a section that has stymied me in the past also brings an "accomplishment smile."
Even in sports I was pretty good at, the correct behavior still becomes second nature, but you still think about where you need to be. The smile comes that 1 in 20 times you back up a play, there is an overthrow, and you throw out the runner trying to advance to next base. That combination of thinking and execution and opportunity always brought a huge (but only inwardly) smile to my face.
For me, I think that is also true of skiing. It's still not like walking for me; I have to think about what various parts of my body should be doing. But sometimes (not often enough) the feeling of knowing I did it well is itself a tremendous feeling.
And I definitely agree with LP about the whole other side of skiing, the feelings and the awe of the beauty of nature. I always remind myself never to get to that point where the act of skiing gets in the way of the experience of skiing; and if I ever ski a whole day without stopping and just looking around, then someone should whack me in the head with their ski pole (gently, please, no concussions).