"A single death is a tragedy, a million deaths is a statistic." Stalin's famous statement is often taken as the epitome of inhumanity - the very opposite of the humane and liberal values cherished in the democratic West.
But when it comes to the war in Syria, the West has been living by Stalin's dictum. So has the rest of the world. Over the past four years, I have written many columns about Syria full of horrifying statistics. One year I noted that 50,000 had died; the next year it was 100,000, the following year it was 200,000. Now the figure may be more than 400,000. One thing that has remained consistent is columns about Syria attract very few readers.
Every now and then, however, a story or an image of an individual tragedy will spark a brief surge of compassion in the West. This time last year, it was the image of the dead body of Aylan Kurdi that sparked an outpouring of anguish.
There was something unbearably touching about the photo, of a three-year-old boy washed up on a beach in Greece, still in his shorts, shoes and T-shirt. Yet there is also something mysterious and capricious about these surges of compassion. At the time, a friend of mine who has reported the Syrian war from its outset, remarked: "I've been tweeting pictures of dead Syrian children for years. Usually, nobody notices."
There has been a similar pattern of capriciousness in the West's reaction to mass drownings at sea. In October 2013, the death of more than 300 would-be refugees in the Mediterranean provoked an international outcry, and prompted Italy and then the EU to step up rescue efforts.
Yet just last week, more than 100 people attempting the crossing to Europe drowned off the coast of Egypt. Their tragedy was barely covered in the western media. The number of deaths in the Mediterranean seems likely to reach a new peak this year, but most of the public seems to have stopped caring.
Western politicians must try to frame a policy towards Syria that takes account of these unpredictable oscillations in public sentiment, between indifference and occasional surges of anguish. Those leaders who have based policy around an assumption that their voters' compassion would be sustained over many months have generally been punished.
Last summer, with many Germans brandishing signs saying "refugees welcome here", Dr Angela Merkel took those words literally and opened Germany's doors to more than a million migrants. But after big gains for right-wing, anti-immigration parties in local elections earlier this month, she has apologised publicly for her refugee policy. Last year's compassion has given way to this year's contrition.
As for Mr Barack Obama, when it comes to Syria, the US president has been accused both of being too callous and too compassionate.
Many American liberals believe his failure to intervene to stop the bloodshed will be a permanent stain on his reputation. But the president is also under ferocious attack from the right for wanting to let more Syrian refugees into the US.
The current outrage over the Russian bombing of an aid convoy in Syria feels like a potential turning point in the Western debate. But past experience suggests that a flurry of interest in Syria will quickly relapse back into confusion and indifference. Mr Obama knows that sudden surges of public feeling are treacherous guides to policy.
The president himself is clearly torn. Last week in a speech to the UN, he praised Alex, a six-year-old American boy, who had written to the White House to offer a home to Omran Daqneesh, a five-year-old, who was the subject of this year's "shock photo" from Syria. Omran had been photographed dazed and bloodied, after being dragged from a bombed building in Aleppo.
"We can all learn from Alex," said Mr Obama.
At other times, however, the US president has seemed fatalistic. As he told the journalist Jeffrey Goldberg, "the world is a tough, complicated, messy, mean place, and full of hardship and tragedy".
The only reliable way for America to stop the bloodshed in Syria would be a large-scale military intervention involving ground troops. After the Afghan and Iraq wars, there is no reason to believe that the US public would support that. There is definitely a constituency in America for "intervention lite" - perhaps a no-fly zone or attacks on the Syrian air force. But this kind of limited intervention, while satisfying the understandable urge to do something, might not do much to improve the humanitarian situation. Syria has had plenty of bombs dropped on it already.
The problem is even more acute when it comes to shelter for refugees. In countries as diverse as Germany, the US, Britain, Hungary and Poland, fear of migrants and refugees - particularly from Muslim countries - has been successfully exploited by populist and far-right politicians.
With Britain on its way out of the EU, Mr Donald Trump dangerously close to the White House and Dr Merkel's political future in doubt, it would be folly to ignore the risks that a more open policy towards refugees could feed the rise of the far-right in the West.
The conclusion is bleak: to sustain liberal politics at home, Western politicians may have to tolerate outrages against liberal values overseas.