"Breaking through from zero to one was difficult, but luckily, once I had something to get hold of, climbing further became relatively easy. It took me a little over two years to more or less sort things out and take some precautions against disrupting space-time, such as changing my face and adding a spell to it that could alter perceptions. And I also discovered some unexpected filth inside my own head: a fragment of Voldemort's soul. It was that fragment that made me realize Voldemort had to die."
Doppelgänger conjured a projection of Harry Potter with his wand and continued, "When that mass of Voldemort's soul that followed me over a thousand years into the past shattered, a tiny piece still entered my body. I became a sort of pseudo-Horcrux that even Voldemort himself knew nothing about. My situation was similar to Harry Potter's. The only difference was that the soul fragment inside Harry Potter could be extracted and destroyed while he was still alive, whereas mine couldn't.
"That fragment of Voldemort's soul had been steeped in the power of time, permeated completely. It was roughly equivalent to a small time bomb. In fact, I was much the same, only far more terrifying-a gigantic time bomb. If either I or that fragment of Voldemort's soul died, this world's timeline would suffer irreversible consequences. The solution was simple enough: first destroy all of Voldemort's other Horcruxes, leaving him with only one possible future-reviving through my body.
"Only then could I lay down my burden, finish a marathon spanning an immense stretch of time, and meet the end I should have met long ago-death. That's right. I wasn't actually freed until the countdown on your chest ended. I designed that countdown. It wasn't particularly attractive, but it should have been clear enough.