Asterix, define 'failed'. Not much territory gained for heavy casualties? Unlike in WW1, Germany's best divisions were in the east at the time, their reserve divisions in the west. The French Plan XVII of WW1 failed on many levels, but primarily because the Germans were prepared for an attack there at the time. In WW2 that was not so. There was a chance at at least limited success, and the worst being a limited failure. What counter-attack or defense-in-depth could a couple dozen German reserve divisions manage against a 40+ division Allied attack through 100's of km of front? Probably not much. Delay them at best, be completely routed at worst.