What does a diplomat do when, after four years, he or she has made little to no progress in ending a war that has claimed the lives of at least 350,000 people and turned an entire nation into a mountain of rubble? For the U.N.’s Syria envoy, Staffan de Mistura, there is only one answer: resign your post and hope the next mediator has better luck.

De Mistura, of course, insists he isn’t departing the job of U.N. special envoy to the Syrian conflict because he’s a quitter or because he has lost patience. Indeed, he’s most certainly not a quitter; the Swedish-Italian diplomat has more than four decades of experience serving the U.N., often in some of the organization’s most difficult assignments. He hasn’t built up such a long career by throwing up his hands when a situation is hard or a few speed bumps block the road to progress. If de Mistura has learned anything after decades of navigating the world’s many conflicts — from Ethiopia in the 1980s, Bosnia in the 1990s, and Iraq and Afghanistan in the 2000s — it’s that patience and determination are vital requirements in the business of diplomacy.

The civil war in Syria, however, would test the patience of anyone. Even a Buddhist monk who lived his life in solitude would grow resigned after spending a few months on the Syria file.

When former U.N. Secretary-General Ban Ki-moon asked de Mistura if he would like to be his personal mediator to the Syria conflict, the veteran troubleshooter was hesitant to take the posting. But after a night thinking about the offer, his hesitancy lifted. As de Mistura told journalist Janine de Giovanni in 2015, he couldn’t simply enjoy retirement when so many civilians in Syria were being killed by merciless combatants on all sides of the war.

Four years after accepting the assignment, there is little de Mistura could cite as an accomplishment. His very first initiative, a six-week ceasefire in Aleppo, Syria’s second city, failed to get off the ground. The shuttle diplomacy he has engaged in hasn’t produced anything but bickering, finger-pointing, and angry denunciations between the Assad regime’s representatives and the political opposition — an opposition that is itself internally divided over negotiating tactics and by the different agendas of their foreign sponsors. De Mistura’s most recent gambit, the formation of a 150-person committee to reform the Syrian constitution, is languishing as the Syrian government objects to some of the participants. Boundless optimism aside, there is still no evidence Syrian dictator Bashar Assad is even remotely interested in playing along with the special envoy’s diplomacy.

De Mistura has made his personal mistakes. It appeared at times that the special envoy was constantly playing catch-up to the facts on the ground, and he had far too much faith in the theory that the combatants were so tired of fighting that they would choose to talk like civilized adults.

But ultimately, not of this is de Mistura’s fault. The reality is that he agreed to take a job that was almost doomed from the moment he scheduled his first meeting. When one side in a war is invested in total victory, when regional powers get involved by funneling weapons to their favorite proxies or launching their own military operations, and when the U.N. Security Council can’t agree on anything but the most watered-down resolutions, not even Houdini would have the tricks up his sleeve to succeed in the position.

Staffan de Mistura is just a human being doing his best. Unfortunately, like his two predecessors in the role, his best could not stop the fighting.

Daniel DePetris (@DanDePetris) is a contributor to the Washington Examiner's Beltway Confidential blog. His opinions are his own.