You probably know that in 1917 the October Revolution happened in Russia: the bolsheviks got power and created the Soviet Union five years later. The revolution split many lives into the "before" and "after" the 1917.
Here is how famous Russian mathematician Dmitrii Menshov tells about those times:
"...In 1915 we studied function series, in 1916 - orthogonal series. And then the 1917 happened. That was a very memorable year in our lives, this year there happened an event that had drastically affected our future lives: we started looking at trigonometric series."
source (in Russian)
I wish I could care that little about anything that's not science :-D