I mean everyone who has a transplanted doujutsu needs to cover it due to the amount of strain it puts on the users chakra, such as kakashi, danzo and that dude with the byakugan with Mei always keep their eyes covered coz it can't be deactivated and consumes a great deal of chakra, so how was nagato able to keep it active all the time without any major strain on his chakra, anybody willing to explain??