people wonder about the how obito couldve gave nagato the rinnegan when he wasnt born when nagato awakened the rinnegan. well i think obito was just lying about to keep up the illusion that he was madara even if it was just in his head. i believe madara gave nagato the rinnegan the same way itachi gave sasuke the amaterasu. it wasnt literal take my eye out and implantthem into your eye socket but more like a transfer. Sasuke amaterasu awakened when he say obitos sharingan and i think madara made his rinnegan activate when nagato would need it most.