Consider this a deadly lesson in the perils of proxy wars. The US has tried to find ways to undermine Bashar al-Assad in Syria ever since the eruption of the “Arab Spring” protests several years ago in Syria, but have lacked the political will to tackle Assad directly. Instead, the Obama administration — reluctantly driven by Congress — has tried finding “moderate” rebels in Syria to arm and carry out the mission on their own. Unfortunately, our friends in Jordanian intelligence tasked with facilitating the transfer of arms decided to enrich themselves instead … and sold the weapons to terrorists who killed Americans and Jordanian police.

The New York Times offers us this reminder of one way in which indirect aggression frequently results in backfire:

Weapons shipped into Jordan by the Central Intelligence Agency and Saudi Arabia intended for Syrian rebels have been systematically stolen by Jordanian intelligence operatives and sold to arms merchants on the black market, according to American and Jordanian officials.

Some of the stolen weapons were used in a shooting in November that killed two Americans and three others at a police training facility in Amman, F.B.I. officials believe after months of investigating the attack, according to people familiar with the investigation.

The existence of the weapons theft, which ended only months ago after complaints by the American and Saudi governments, is being reported for the first time after a joint investigation by The New York Times and Al Jazeera. The theft, involving millions of dollars of weapons, highlights the messy, unplanned consequences of programs to arm and train rebels — the kind of program the C.I.A. and Pentagon have conducted for decades — even after the Obama administration had hoped to keep the training program in Jordan under tight control.

The Times distinguishes this program from the spectacular failure of a similar CIA effort to fight ISIS, one that spent $500 million to train 60 people … only five of whom survived. This program began in May 2013 and has trained “thousands” of rebels, and the CIA considered it a successful effort — until the Russians reinforced Assad last year and reversed the rebels’ gains.

The weapons come from eastern Europe, with the Saudis providing a big chunk of the cash and the US providing the expertise. Neither country wanted to commit ground troops to the anti-Assad coalition, preferring instead to sponsor native bands of fighters to the cause. That decision made some sense in that it prevented either country from getting bogged down in what would inevitably be an Iraq-esque occupation, dealing with a dispersed insurgency in a post-Assad era sponsored by Iran.

However, the protracted nature of the conflict and the vacuum it created opened up an opportunity for al-Qaeda in Iraq to metastasize into ISIS and seize control of the Syrian-Iraqi desert, creating a global disaster out of what had been a regional problem. On top of that, we now find that we’ve been arming some of the groups that oppose the effort, thanks to corruption within Jordanian intelligence, and that it’s cost American lives.

Sometimes, the way to win these games is not to play. Of course, that means refraining from drawing red lines and encouraging rebellions when one has no stomach for waging war to support them, too. We didn’t learn that lesson in Libya, and we’re still not learning it in Syria.