I'll admit I know little about the French army at the time, what was this cult of the offensive that I saw mentioned?
Basically the French believed the best way to beat Germany was to seize the initiative and constantly attack as well as maintaining high morale. They believed war was primarily a battle of morale and as long as they maintained high morale and constantly attacked they could beat Germany who was stronger industrially and militarily. Of course this failed horribly because it was a thinking far more suited to the 19th century than the 20th.
Also Flocculencio I just started reading Guns of August along with finishing A World Turned Upside Down, and that inspired this thread. Being a bit of a Francophile I'm saddened by how ingrained ignorance of the realities of modern war were ingrained in French Military thinking.