Board Thread:Theories and Speculation/@comment-27082825-20150116155842/@comment-25626003-20150121222133

BeyondRed wrote: Haven't seen it brought up yet, but the anime has been making up rules on nature transformation for a long time. In episode 63, Yamato claims that shinobi have secondary and tertiary affinities (not sure about the actual term he uses) aside from their main one. His explanation fairly explicitly states that you have to be born with a nature in order to acquire it through training, otherwise you can never use it. Naruto asks if he can eventually learn Water Release, and Yamato tells him he'll have to find out if he was born with it.

Of course, we have since learned that isn't the case, just like his other statement from that same episode that no shinobi can use all five natures. On his other statement, it's highly plausible that Yamato simply didn't know it was possible. Before the databook came out, the only shinobi we knew obtained all 5 natures was Hiruzen, and that was WELL after the episode you're referencing. In my opinion, it's an anime mistake because in episode #393 it's clear that it's possible to learn all 5 elements through training if you're skilled enough, regardless of what your "affinity" is. It's just that your "affinity" is what you'd be best at, like Kakashi with Raiton and Naruto with futon. Hell, the anime shows that raiton is Sasuke's elemental affinity, but because he's an Uchiha and that it's anime we ignore that fact. End point being, the anime shouldn't be discounted.