Hi BraveBlueMice,
I can see your point that it's all about energy flow.
I'm not sure I agree with your pebbles theory though. What follows is my own opinion, and understanding on the matter, not claiming it's gospel truth or anything.
Moving both pebbles, or better yet, not trying to move either pebble, but allowing them to move in accord with their own nature as they will .. aligns us with the natural flow of the universe, the 'force' around and within us.
Mentally, trying to push one before the other, impedes flow.
In fact, being open, and not using mentality to force an issue (or to push a pebble), opens us up to more, higher energy within the cosmos. Forcing things, either physically, or mentally with our mind, closes us down. It's like trying to make water come out of a hose faster, by squeezing or contorting it.
In my mind, being natural and allowing both to move, according to their (your own) natures, is more balanced and in harmony. The alternative is one-sided. In Taoism, it's like trying to be fully yang, or fully yin, it will make you unbalanced and will tire you (less energy). Also in Taoism, you may have seen the yin-yang symbol, the little white and black dots, mean that extreme yin, or yang, turns in to it's opposite ...