Much like the Napoleonic invasion of Moscow, the key was home field advantage. Not in the classic Russian winter sense.
Once Napoleon's army arrived in Moscow, there was a "what now" aspect to the war. They'd accomplished the goal that was set out and defeated Russia, but they didn't actually want to live in Moscow. So, they eventually left to go fight the Russian army, which had seemingly and unbelievably abandoned its crown city to the invaders. But they hadn't. Because Moscow was home, whether it was filled with these unseemly visitors or not. There was no way Napoleon's forces could win unless the Russians actually decided to sign a piece of paper and let them.
Once Napoleon's army arrived in Moscow, there was a "what now" aspect to the war. They'd accomplished the goal that was set out and defeated Russia, but they didn't actually want to live in Moscow. So, they eventually left to go fight the Russian army, which had seemingly and unbelievably abandoned its crown city to the invaders. But they hadn't. Because Moscow was home, whether it was filled with these unseemly visitors or not. There was no way Napoleon's forces could win unless the Russians actually decided to sign a piece of paper and let them.