How do drone strikes go wrong?
However impressive technologically advanced weapons are, they still rely on human beings to guide them. That's where missions go awry.
Two hostages, Warren Weinstein, an American, and Giovanni Lo Porto, an Italian, were killed in Pakistan.
Mr Obama says he takes "full responsibility" for their deaths.
The loss of these two men shines a spotlight on the efficiency of US operations. White House officials have provided few details about the raid, but few doubt that it was a drone strike.
Officials have said for years drone strikes are precise. But no matter how sophisticated the machines are, they're still controlled by humans.
That's usually where the problem lies.
Mistakes happen, says William Banks, a professor at Syracuse University's Institute for National Security and Counterterrorism, largely for one reason: "People are involved."
In most cases the people are good at their jobs. Over the years the drone programme has been extraordinarily effective in the fight against al-Qaeda. Dozens of al-Qaeda commanders have been "taken off the battlefield," as Mr Obama puts it, through the strikes.
Mr Obama recognised the dangers of the programme and had a policy that stated no strikes would be carried out unless there was "near certainty" that civilians would not be killed.
The process for carrying out a drone strike is complex, though, and critics of the programme say it was only a matter of time until they backfired.
People in Pakistan - officials as well as individuals who are hired locally - help US analysts put together information about the hiding places of militants.
In addition, individuals who work on the drone programme, whether they are CIA analysts or done pilots, sift through intelligence from satellite imagery, audio recordings and other sources in order to distinguish "bad guys from good guys", Mr Banks explains.
"Even if you're up close and personal, it can be difficult," he says, "much less if you're at a distance, using technical means."
They examine images and video footage over a period of time and then make a decision about whether to carry out a strike.
At times mistakes occur because of poor judgement. Analysts may, for example, assume that the individuals who are living or working at a militants' compound belong to the organisation.
As one official told reporters for the New York Times: "Al Qaeda is an insular, paranoid organisation - innocent neighbours don't hitchhike rides in the back of trucks headed for the border with guns and bombs."
Americans believed that only militants were living in the place that was attacked. The people who selected the target simply didn't know the hostages were there.
The deaths of Mr Weinstein and Mr Lo Porto are tragic - but are unfortunately not a shock for those who are experienced in these kinds of operations. At times the data - and the assumptions of analysts - are wrong. There have been near-catastrophes in the past.
An American journalist, David Rohde, was kidnapped and held hostage in Pakistan - and was himself nearly killed by a drone strike in 2009. A missile landed near the house where he was kept.
Afterwards he wrote: "The plastic sheeting covering the window hung in tatters."
Other times the missiles hit the wrong target.
More than 250 civilians have been killed in drone strikes in Pakistan, according to data compiled by the New American Foundation, a research organisation based in Washington.
Pakistani officials said the tragedy "demonstrates the risk and unintended consequences of the use of this technology".
In the case in which Mr Weinstein and Mr Lo Porto were killed there was "faulty intelligence", says Jordan Paust, an international law professor at University of Houston. Still, he says the site appeared to be a "lawful target", despite the unintended deaths.
"Someone's got to make a choice," he says. "That's not necessarily a war crime."
Obama and his deputies have for years touted the accuracy of drones, while ramping up their use. They've also downplayed the flaws in the drone programme.
Now that the botched raid has been revealed, however, they may have a harder time making a case for the efficiency of their counterterrorism efforts