Please pardon if this has already been asked.
I'm confused about one point, according to what I have read, only individuals who are spiritual are able to bend. This is why Sokka can't bend. Now what confuses me is this, according to Katara or some other character (I believe this is when they were at The Northern Water Tribe), water benders learned to bend by watching the moon. If this is the case, can't anyone just do that and water bend ? For that matter can't anyone just pick up bending if they really tried ? My theory is that originally all benders were energy benders who became specialized in a particular element (I believe this was mentioned by The Lion Turtle.). Any thoughts ?