Stalin managed lots of things; like selling Germany steel up until the morning of the German invasion. Churchill famously reminded Stalin of this fact when Stalin went into one of his infamous telegraph tirades demanding more of the Arctic convoys shipping materials from the US and Canada to Britain be redirected to Russia.
Russia did not survive WWII all on its own. It too was a beneficiary of Western aid; both directly via Lend Lease, as well as aid in gaining control of the Trans-Iranian Railroad, and ultimately opening the Second Front with the Normandy Invasion, which finally forced Germany into the nightmare two-front war.
Russia has never been as invincible as it liked to portray itself. Even when it ultimately drove out invaders, the costs were massive.