They said it would be over by Christmas. Over the last century it's almost become cliche, a term for foolish over-optimism and a complete failure to assess the enemy.
Over by Christmas: Ten million soldiers and five million civilians died over the next four years - about 4% of the population in France and Germany. Most of the military deaths happened in the trenches of course, where a combination of mass produced artillery and machine guns turned No Man's land into a meatgrinder.
In the air it was different, especially in the beginning. Flying was a danger in and of itself and the pilots on both sides often felt more camaraderie for each other than the poor fellows on the ground. Initially armed with pistols and rifles, two 'combattants' might take a few shots at each other, but any actual hits or damage was besides the point. Incidental.
That would change of course. The Eindecker would pave the way and soon machine-gun armed scouts made recon and artillery sighting dangerous occupations. Then the scouts turned on each other. Getting shot was, of course, bad enough but the real fear was fire. You had no parachute: Did you let yourself die in flames or jump and shatter on the earth a kilometer below?
DiD campaigns let us try to mimic the campaigns these people fought in. This isn't about accumulating victories. It's not about glory. This is about seeing your mother/wife/girlfriend/dog one more time. It's about returning to your home village and being able to say 'I was there.' It's about taking this terrible madness that the lords of Europe have started, and using it to tell a story. Your story.