In her speech yesterday, Michelle Obama talked in personal terms about her own and President Obama’s modest upbringings. She discussed her own father’s struggles as a pump operator to put her through school and Obama’s grandmother and single mother, who suffered pay discrimination. She talked about how student loans enabled both Obamas to eventually enjoy lucrative careers.

“When it comes to rebuilding our economy, Barack is thinking about folks like my dad and like his grandmother,” Ms. Obama said.

This biographical detail has been widely interpreted as an effort to forge an emotional bond with working and middle class Americans — a reminder that the Obamas have experienced what they have, while the Romney’s haven’t.

But it’s also worth noting that the implicit biographical contrast Ms. Obama drew here is directly relevant to one of the central policy disputes of this campaign — the argument over how best to create opportunity and shared prosperity.

How should we rebuild our economy to create opportunity for those who lack it? The two candidates have starkly different answers to this question. Romney believes the best way to promote opportunity is to unshackle the free market, which will enable people to realize their potential and shower everyone with prosperity. His running mate’s fiscal vision entails deep cuts to education and financial aid for students. Romney has counseled struggling students to shop around and borrow money from their parents. Obama derides this as “you’re on your own economics” and says recent history has shown this to be a sham.

Obama, meanwhile, is arguing for a larger governmental role in facilitating opportunity, through more investment in education and financial aid and other judicious government intervention in the economy. Romney derides this as favoring government-enforced “equal outcomes” and claims Obama’s argument for government support is demeaning of individual initiative as a factor in people’s success.

Romney cites his own success as proof of what the private sector can shower on people if only we allow it to. Obama, too, has cited himself as the type of person who needed assistance in order to fully realize his potential; Ms. Obama’s speech fleshed that out last night. In other words, both cite their own successes in making the case for how to make the economy work for everyone. But the key difference is that Romney went on to enormous success after growing up amid far more comfortable circumstances than the Obamas did.

Michelle Obama’s speech wasn’t just about emotionally connecting with the middle class. It was about driving home that she and Barack have lived through some of the same life experiences as the people who are at the center of the campaign’s policy dispute over how to promote social mobility, shared prosperity, and economic security.

This isn’t to detract in any way from Romney’s achievements; he seems to be an extremely hard worker with a great deal of self-discipline. Rather, the point is that if both are going to cite their own stories as proof that their vision is the best way to promote opportunity and mobility for those who lack it, the Obamas have a far more relevant tale to tell.