The context in with the sentence stands is that around that time there was the believe that the Germany army counted on being supported by other German institutions and those institutions didn't support the army but failed the army.
This is commonly known as the stab-in-the-back myth. "Myth" as the winners of WWII wrote our history books. There nothing inherently irrational about that sentiment even though it might have been wrong.
It's not about blaming the troops. If something seems so stupid that it doesn't make sense to you, it might be that the problem is on your own end.
No plans were made for a war even one year long (although highly placed individuals had their doubts and are now widely quoted about it). No German (or other) plans which existed at the start of WW1 were relevant to the way the war ended many years later. Conversely, whatever accusations were made about betrayal in the later years of the war were clearly irrelevant to the way those plans played out in 1914 when all Germans were united behind the war effort, including Socialists.
Another month, another rationality quotes thread. The rules are: