Hiring the wrong people
Another good reason why a perfectly workable strategy doesn’t work is because you hand it to the wrong person to execute. Often times, implementing a new strategy involves hiring or promoting an employee specifically tasked with executing that particular strategy.
But if you get the hiring wrong, then the strategy fails as well, or at least appears to do so. And because hiring is a difficult process, people just dump the strategy rather than go through the entire hiring process again.