why didn't something happen at the beginning when Madara applied Hashirama DNA into his body?
is Senju DNA really the solution?...
i believe that Senju DNA might be one of the head ingredients, but i kind of think that there is something else that must be added to the mix...
Sharingan...
Mangekyo Sharingan...
Eternal Mangekyo Sharingan...
all these 3 evolve after certain feelings... hatred... loss... sadness... you know this already right?
Madara didn't get Rinnegan as soon as he applied the Senju DNA, he didn't achieve it until near death...
perhaps this is the reason for unlocking the Rinnegan...
To finally forgive yourself, to accept yourself for who you are and get rid of all that hatred towards other people... to accept what has happened and that your brothers will never come back... to finally get that feeling that no matter what you do now, there's nothing else that can be done, you're finished... finally... you've done all you can and it's finally time to say goodbye?
you see, Madara had already got Rinnegan before he met Obito for the first time... so i think that Madara had already realised that he was going to fail with his plan... his plan to not become the Hokage of The Hidden Leaf... but to become the leader of the whole world instead... it was all a fail and Madara had finally accepted that. therefore unlocking the rinnegan... when Madara unlocked the rinnegan he gained a tiny bit of new hope, implanting the rinnegan in someone elses body... (and let Zetzu make Obitos work... and let's face it.. that wouldnt've been possible because i don't think that Nagato would've Negotiate without a fight)
not until finding Obito did Madara regain the true hope for his dreams to come true, because finally did he find someone trustworthy and someone that could actually help him with his plans... of course did Madara already have a tiny tiny bit of plans but Obito was the key to everything...