Board Thread:Theories and Speculation/@comment-28717679-20160611095118/@comment-9782468-20160611221826

Basically to summarize, Kakashi said most Jonin can use at least two, not up to two. Kakashi himself is a prodigy of a ninja (compared to the normal shinobi of Naruto), and was able to learn every nature. When Kakashi uses the Sharingan to copy a technique, he already has the skill to use the technique. The Sharingan just lets him see exactly how it's done, and he takes it from there.