A "Hail Mary" pass is the last act of a team facing defeat. The pass entails the QB loading the secondary - the offence behind the line - with 5 receivers.
This tactic https://en.wikipedia.org/wiki/Hail_Mary_pass while overloading the defence with men capable of catching high balls leaves the QB with NO protection.
This play is only used in extreme conditions, such as trying to win a game with one play left.
Each day, we read that ISIS is getting pushed further back and suffering heavier loss - they are so scared of losing, they buried 44 of their own men for attempting to flee this week.