blind alley -
(figurative) a course of action that is unproductive and offers no hope of improvement; "all the clues led the police into blind alleys"; "so far every road that we've been down has turned out to be a blind alley"
course of action,
course a mode of action; "if you persist in that course you will surely fail"; "once a nation is embarked on a course of action it becomes extremely difficult for any retraction to take place"
blind alley -
a street with only one way in or out