So many things would have changed for the better in that war if the various actors had drawn clear lines in the sand in advance.

E.g. the Germans believed the British wouldn't go to war with them over Belgium, the British knew Belgium was under threat in advance, but wouldn't draw a clear line in the sand telling the Germans that violating Belgium was an act of war.

Likely doing that would have kept Britain out of the war entirely since Germany would have attacked France directly.