What if Fanny Kaplan was a better shot?
On August 30, 1918, in front of a Moscow factory, Kaplan fired three shots at Vladimir Lenin. One missed, two didn't. Lenin wasn't killed, but was injured sufficiently enough that it led to deteriorating health and death in 1924. Kaplan was executed four days after the assassination attempt.
Now imagine Lenin was killed on the spot. In 1918, it's unlikely that Stalin comes to power. Russia, already in disarray and fighting a Civil War, would destabilize further. Who rises to the top? Is there even a Soviet Union? Do the Bolsheviks prevail? What happens to Stalin, Trotsky, et al? A different path for Russia pretty much means a different path for the entire world. What about the Great Purge? World War II? The Cold War? Etc, etc, etc.
But, you know, they don't teach sharpshooting to Jewish girls.
All things considered, it's probably for the best?