The death of two hostages during a rescue attempt in Yemen shows how little room there is for bad intelligence or bad luck when U.S. forces go into action on such high-risk missions.
Faulty intelligence doomed a raid in Syria earlier this year to rescue American journalist James Foley, who was not where he was thought to be and was subsequently beheaded in August by Islamic State militants.
British aid worker Linda Norgrove was accidentally killed by U.S. soldiers in Afghanistan in October 2010, though the team's initial report blamed her captors for the grenade that caused her death.