It was stated by Kakashi that he "trained" in order to get his Mangekyo Sharingan. But after reading this chapter I came tot he conclusion that Tobi is the reason why Kakashi developed MS himself.
Both Tobi and Kakashi have the same Mangekyo pattern. When we see Sasuke, Itachi, Madara, and Izuna develop their MS both eyes change at the same time. I believe this is the reason Kakashi obtained his mangekyo. Sharingan eyes are linked it is my belief when one develops into the mangekyo the other one does as well.
Although they both develop at the same time, one eye will become more advanced than the other. For example Sasuke was more skilled with his left eye when he fought Bee, but learned to use his right eye while fighting A.
I'm not saying this is the definite reason, I'm just saying this is what Kishimoto might be implying to us.
You must be registered for see images
Both Tobi and Kakashi have the same Mangekyo pattern. When we see Sasuke, Itachi, Madara, and Izuna develop their MS both eyes change at the same time. I believe this is the reason Kakashi obtained his mangekyo. Sharingan eyes are linked it is my belief when one develops into the mangekyo the other one does as well.
Although they both develop at the same time, one eye will become more advanced than the other. For example Sasuke was more skilled with his left eye when he fought Bee, but learned to use his right eye while fighting A.
I'm not saying this is the definite reason, I'm just saying this is what Kishimoto might be implying to us.