The failure was due to a fentanyl overdose that killed a significant number of the hostages. Two comments: 1) The technique may well have been refined since then, and 2) I don't care too much if they kill some of the terrorists by accident. They aren't hostages.
Besides, it's likely a painless debt... fentanyl overdose leads to unconsciousness followed by breathing failure due to breathing center suppression.
But what if no one kneels on your neck????
;-)