Thats how blitzkriegs work

The first 3 days are critical. You need to smash a hole deep in the defence. Then gather logistics to carry on. however you are horrifically exposed until you shore up your flanks.

if you don't break the spirit of the defenders then you're in deep shit.

for what its worth, the german invasion of france almost failed, because the entire column got bunched up in the Ardennes. Had the french acted in time, the germans would have been destroyed.

Plus, because the french were so motorised it allowed the germans to piggyback on the infra.