I can't understand why members of the the Triple Entente and also members of the Triple Alliance were so offended by the mere mobilization of their enemies' armies, so that they demanded a cessation of mobilization or else they would declare war.
Why not simply decline to meet trouble half way, and match mobilization with mobilization, putting the ball back in the other nation's court, so to speak.
For example, Wikipedia: World War I says:
"The Serbian capture of ports on the Adriatic resulted in partial Austrian mobilisation on 21 November 1912, including units along the Russian border in Galicia. In a meeting the next day, the Russian government decided not to mobilise in response, unwilling to precipitate a war for which they were not yet prepared."
This quote seems to imply that to mobilize one's army, even partially, and only to match partial mobilisation with partial mobilization was tantamount to a declaration of war. I don't see why it should be.
And when Russia did eventually mobilize, Germany did declare war on Russia, rather than take the measured, defensive response of likewise mobilizing.
The Great War Series has "Why Did The First World War Break Out? (July Crisis 1914 Documentary)"
Youtube at 21:25 / 30:26 has
"[…] and thirty minutes later Germany announced their mobilization. By seven pm Moscow told Berlin that Russia would not stop its mobilization, and so Germany declared war on Russia."
I don't see how that follows.
Wikipedia: Mobilization#Mobilization in World War I which (interestingly, I think, but does not answer to my satisfaction the question I am asking), says:
"Intricate plans for mobilization contributed greatly to the beginning of World War I, since in 1914, under the laws and customs of warfare then observed (not to mention the desire to avoid compromising national security), general mobilization of one nation's military forces was invariably considered an act of war by that country's likely enemies."
So it's not a question of simply "Why didn't Germany do things differently on that day?" but rather, why was mobilization seen as an act of war by everyone at that time?
It seems to have contributed to the danger of war breaking out accidentally. It's not specifically about Germany, but that kind of thinking by countries back then, of which the German demand and subsequent declaration of war on Russia on 1st August 1914, when that demand was not met, is a well-known example.