Germany attacked in 1914, because she knew Russia was modernizing rapidly, and it was a classic case of “now or never”, they estimated that in five years it would be impossible to defeat Russia.==
History proved it was impossible even in 1914. Look what happened with Germany?
Russia may lose a battle or 2 but she always come again and again until enemy is defeated. 1000 year of history and 1000 different wars.
With hindsight, of course, but that was truly what the Germans believed then.