By the end of the first night of the Democratic National Convention, many journalists and others watching these festivities and last week’s Republican jamboree had had enough. From both left and right there came a bipartisan consensus of kibitzers crying out for a halt to the endless stream of narratives about impoverished or difficult upbringings overcome by hard work and all the other all-American virtues that lead to success. Many a commentator noted that if they had to listen to one more sob story about growing up poor they would scream. Others facetiously promised that after the binge of Horatio Alger tales that they had been subjected to, they would support any candidate, whether liberal or conservative, who would avow they were born to privilege and had squandered a fortune due to laziness and indifference.

These understandable sentiments are the inevitable product of the repetitious nature of the speeches being aired at both conventions. Though Republicans and Democrats disagree on a great deal they all seem desperate to convince us they were born in the moral equivalent of a log cabin and that their emergence from their humble beginnings entitles them to our admiration as well as our votes. But as tiresome as this rhetorical feedback loop may be, we ought not to complain too much about it. The reason why politicians feel the need to say these things and why, despite our grousing about it, so many of us long to hear it, is rooted in our national identity. Social mobility is not, despite the efforts of some on the left to disparage the notion, a myth. It is at the core of what means to be American and though we may laugh about it, it is vital that we continue to celebrate it.

American exceptionalism is not just a foreign policy concept but also a fundamental principle of our domestic politics. The notion that any American, no matter what their parents did or where they came from, can reasonably aspire to wealth as well as to political prominence is what has also made the United States unique. Even as Europe and parts of the rest of the globe transitioned to democracy, the notion of caste remains strong elsewhere.

It is true that Americans are not immune to the siren song of inherited privilege. We love foreign royals and treat certain American families as if their last name was Windsor instead of Kennedy or Bush. We also know only that no one is guaranteed a shot at fame, fortune or power and that far too many fall short of their aspirations and remain mired in poverty.

Yet the reason why both Republicans and Democrats like to talk about pulling themselves up by their bootstraps is because it is not only possible to do so in America but that those who achieve such a success are not considered outliers, as they would be elsewhere. That’s why immigrants continue to flock to our shores. They want a piece of that American dream that earlier immigrants seized for their posterity. To the extent that we undermine the chances of the poor to do so by liberal social welfare policies that trap them in poverty and dependence and undermine their incentive to succeed, we not only betray them but our national ethos.

It should be noted that the most famous person to rise from a log cabin to the White House was actually disgusted by the way his supporters spoke incessantly about his origins. His most astute modern biographers note that Abraham Lincoln may have been elected as Honest Abe the rail-splitter but he spent his adult life trying to flee the abject poverty into which he was born. Members of social and political elites did look down their nose at him but he prided himself on his self-taught erudition as well as having become one of the better-paid members of the Illinois bar by the time he was elected president. Lincoln had to listen as his supporters carried on about the flimsy shelter where his mother brought him into the hardscrabble world of what was then called the American west, but such talk made him cringe.

We have come to primarily associate Lincoln with his inspired leadership and rhetoric during the Civil War and in particular with his role in ending the nightmare of American slavery. Yet it is a mistake to ignore the importance of his origins in the building of the Lincoln mystique. Lincoln truly had come from the lowest strata of American society at a time when the overwhelming majority of those in politics were to the manor born. His rise embodied the possibilities of the republic he led and while some still call it a myth, we know better.

Some of the men we’ve elected to the presidency in the last century were born to privilege and wealth. The Bushes, John Kennedy and the Roosevelts certainly qualify in that category and Mitt Romney would join their ranks. But more have not. Harry Truman, Dwight Eisenhower, Lyndon Johnson, Richard Nixon, Ronald Reagan, Bill Clinton and now Barack Obama all started out in life a lot closer to the bottom than the top rung. Some, like Jimmy Carter and Gerald Ford, belong somewhere in the middle.

Initial poverty is not a qualification for the presidency or any office and Americans have usually been smart enough to know that it is better to have a capable swell in the Oval Office than a fool or scoundrel born in a log cabin. But we ought never to stop celebrating upward mobility and the value of the individual effort that makes it possible. To do so would mean we were truly on our way to a social democratic model that valued ideas about equality but not the American dream. And if that means having to listen to tedious poverty narratives at our political conventions, so be it.