Board Thread:Theories and Speculation/@comment-27916438-20170329044844/@comment-734582-20170411182746

Starscream1998 wrote: Itachi explains that the moment the power of the Mangekyo is obtained that power slowly begins to shut itself down so yes it is a feature. Itachi also said that Madara was the first to awaken the Mangekyou, and that he killed his clan as a test of power.