I recently visited a Special Operations headquarters in the Middle East—the location, along with other details, must remain classified. I received an incredibly impressive briefing on how U.S. commandos generate intelligence, locate targets, and then swoop down on them. The “operators” are the model of manly understatement. They don’t brag but convey a quiet confidence that they know what they are doing—and they do.

As has been reported in several outlets, the Joint Special Operations Command—which comprises Navy SEALs, the Army’s Delta Team, Army “Night Stalker” helicopter crews and other, even more clandestine forces—carries out a dozen operations a night in Afghanistan alone. Other JSOC contingents carry out raids in Iraq, Yemen, Somalia and other lands where al Qaeda and its ilk operate. Most of these operations go so smoothly—resulting in a “jackpot,” a wanted suspect killed or captured—that there is no mention of them in the press.

JSOC—and the entire U.S. Special Operations Command, of which JSOC is only one element—has come a long way since the 1980s. It was formed then in the wake of Operation Eagle Claw, the Iranian hostage rescue mission that resulted in disaster at a rendezvous point code-named Desert One.

Robert Gates was working at the CIA at the time, and as secretary of defense earlier this year he feared that the U.S. raid on Osama bin Laden would turn into another Desert One. His fear was understandable but misplaced. Such operations have become much more routine than they were in 1980. Since 9/11, JSOC has become the most experienced and capable special-operations force the world has ever seen.

Yet things can still go wrong, especially when the element of surprise is lost. Normally the enemy has no idea when the raiders are coming, since they descend from the night sky and surround their targets before they have time to respond. But it’s different when another special operations element is caught in a firefight and a Quick Reaction Force is sent out to rescue them.

In 2005, a SEAL team was caught in a firefight in Kunar Province in eastern Afghanistan. A Quick Reaction Force aboard a lumbering Chinook transport helicopter was shot down by the Taliban with a rocket-propelled grenade, killing all 16 on board. (The only SEAL to survive that harrowing mission, Marcus Luttrell, was part of the ground element being rescued and subsequently wrote a best-selling memoir, “Lone Survivor.”)

History repeated itself on Saturday. Another U.S. contingent was caught in a firefight—this time in the treacherous Tangi Valley south of Kabul—and another Quick Reaction Force of SEALs was sent out in a Chinook helicopter. The Taliban, undoubtedly knowing the SEALs were on the way, used another rocket-propelled grenade to bring down the giant helicopter. This time the loss of life included 30 Americans, most of them members of the ultra-elite Seal Team Six, along with eight Afghan counterparts.

The loss underscores how heroic these men are—volunteers multiple times over who give up hope of a normal life to spend month after month deployed in one war zone after another chasing some of the most dangerous terrorists on earth. They know the risks they run: All Special Operations headquarters have a “wall of honor” displaying the pictures of fallen heroes—all supremely fit and dedicated young men struck down in the prime of life. Yet their comrades routinely strap on body armor and mount helicopters, night after night, knowing that their picture could soon hang on that wall.

While we should be in awe of special operators and their accomplishments, we should keep their capabilities in perspective: They cannot win a war by themselves.

The Tangi Valley is an area infested by Taliban. Even if Saturday’s raid had been a success, killing or capturing some local Taliban leaders, it would hardly have ended the insurgent threat in that area. Counterterrorism raids are a vital part of any integrated counterinsurgency strategy, but they cannot substitute for the lack of such a strategy. The loss of leaders hurts any organization, but terrorist groups like the Taliban—or al Qaeda or Hezbollah—have shown considerable ability to regenerate even after major losses.

Only one thing can lead to their decisive defeat: a critical number of boots on the ground. In Afghanistan, the U.S. and our allies have the necessary ratio of ground forces in only two provinces—Helmand and Kandahar. The rest of the country is an “economy of force” mission. U.S. commanders hope to shift resources from the south, once that has been secured, to the east to gain control of ungoverned areas. But that strategy has been thrown into jeopardy by President Obama’s decision to pull out 30,000 U.S. troops by September 2012.

Many in the administration wanted an even more precipitous withdrawal, arguing that we could rely on Special Operations troops to keep our enemies from establishing control of critical terrain. Saturday’s disaster shows the risks of that strategy and underlines the limitations of even the world’s best special operators. So we should honor them, but we should not exaggerate what they can do.

Mr. Boot is a senior fellow at the Council on Foreign Relations. He is completing a history of guerrilla warfare and terrorism