[@Bishop] Just because you can't [i]use[/i] them doesn't mean you don't have them. Everyone has 5 natures. But you are more inclined to 1 nature, and then a second, and then a third, and then a fourth, and [i]then[/i] a fourth. Now consider that most people only ever unlock 3 of them during their lifetime. 

Therefore, it's very impressive that Hiruzen managed to use all 5 [i]at a master level.[/i]