Gaining access to the Sharingan isn't easy; in fact, it's more of an ordeal. Physically, using the Sharingan requires a lot of chakra. In the series, we see that this is a huge to-do for non-Uchiha like Kakashi and Danzo, who have to cover their Sharingan when not in use. Otherwise, since they can't deactivate it, the power will drain all of their energy. However, one of the most significant potential physical setbacks for the Sharingan is that it can cause blindness. It's that reason why one of the untold truths about Sasuke is the fact that by the end of "Shippuden," he doesn't have the eyes he was born with. Awakening the Mangekyō form of the Sharingan causes enough physical strain on the eyes for blindness. So, in Episode 216 of "Shippuden," he replaces his own eyes with his brother Itachi's.
Still, the setbacks to the Sharingan don't just end with physical detriments. There is one significant emotional setback, too. To even evolve a Sharingan to the Mangekyō Sharingan form, one must experience a traumatic loss. One of the most heartbreaking examples of this takes place with the tragic character Obito Uchiha. During "Naruto" Manga Chapter 605 (via Viz), Obito witnesses the inadvertent death of his childhood friend, Rin Nohara, by Kakashi. The devastating event not only gives insight into why Obito becomes a villain but also awakens his Mangekyō Sharingan. It's a great power for Obito, but at what cost?
