Board Thread:Versus Debates/@comment-2245550-20160522071949/@comment-2245550-20160523095606

A kekkei genkai can't be copied because, unlike any normal jutsu, it's in the bloodline itself. If you don't have the DNA, you can't do it. And that makes sense, though learning how to perform nature jutsus is mostly easy, some are easier than others. When you've learned how to utilise your chakra into becoming one of the five natures, the Sharingan can have you copy every jutsu you see of that same nature, thus allowing you to easily master that nature and all others by following the same process. So technically, it was easier for Kakashi, since Hiruzen mastered the five natures through extensive training.