In reality, the French assumed a dense forest north of the Maginot live was impenetrable by armored forces, or at least that they would have to go very slowly, giving the French army plenty of time to stop them. They were wrong.
They also assumed that Belgium and The Netherlands fortifications would be able to make things difficult for German forces. Wrong again.
France's fundamental problem though was the same as that posed for Britain and other countries. Although few experts saw the change coming in full, it was obvious before the outbreak of WW II, that new technology, equipment, weapons, organization, and tactics would tend to renew the potency of mobile warfare.
As it was, in the first phase of WW II, blitzkrieg war, or combined arms tactics as it is now usually referred to, make it possible to defeat much larger but unprepared armies and to go around or destroy even the most formidable of fortifications.
In the German invasion of Belgium, highly trained special forces quickly blew up or captured Belgium's border fortifications. And in the attack through the Ardennes, French resistance was quickly overcome through surprise and combined arms tactics. Even the main French mobile force in Belgium was easily defeated and put to flight.
yep, the nazis just drove around the end of Maginot line ... i guess they ignored the sign at the Belgium end of the fortification that said “Do Not Drive Around” ...
[same tactic the USA used during against Iraq during Desert Storm]