Undoubtedly, this is a result of the confusion
the enemies sought to sow in Jerusalem (Nehemiah 4:8) through whatever means. Once the people in the city heard not only of plans to attack but also that they will never know of any attack until it is too late, enthusiasm for the work was bound to diminish (as the enemy intended).
11 And our enemies said, “They will not know or see till we come among them and kill them and stop the work.”