Board Thread:Wiki Discussions/@comment-24772621-20140404025706/@comment-26302001-20140404165056

It is shown that the further back in time the person died, the more chakra it takes for the technique to bring him/her back.. Which is why Obito was doomed to die when bringing back Madara. Nagato did not know the rinne tensei then either, Obito taught it to him after the fact.