Well, I’ve often said that wars are won by the side that has the most crazy bastards on their side. It’s one thing to be smart, but it takes a particular kind of batshit-crazy out-of-the-box dirty fighting to win a war.
My favorite example is the Enigma codes. The Allies finally got their hands on one of the Navy machines, and cracked the code but good. Do they use this to intercept battleships and blow them out of the water left right and center? No. If they’d done that, the Axis would have realized their mail was being read, and would have switched to a different code system. Instead, we targeted their supply logistics, targetting supply ships carrying kerosene for tanks. Soft targets, that just happened by ‘random chance’ to run afoul of a lone destroyer out on patrol, while our own supplies slipped through with confidence. The result being that the tanks that were a primary focus of Axis power were crippled.
But yeah, France just wasn’t expecting that. Conventional warfare at the time stated you attacked ONE country at a time, so as not to fight multiple fronts. The idea that you would push into a country just enough to flank an opponent? Unheard of. It would be like playing football and the other team charged through the stands to the goal.