If fighting is sure to result in victory, then you must fight, even though the ruler forbid it; if fighting will not result in victory, then you must not fight even at the ruler’s bidding. — Art Of War X:23The generals could not have feared the Führer to the point of not heeding that sound military advice, could they have?
Even some of the generals told Hitler not to retake the Rhineland.
Everytime Hitler got away with it (Rhineland, Sudetenland, Austria, Czechoslovakia), the generals knew that opposing Hitler was pointless when it came time to execute “Fall Weiss”.