Some 45 percent of food stamp recipients are children, for example. Do we really think that kids should go hungry if they have criminal parents? Should a little boy not get a curved spine treated properly because his dad is a deadbeat? Should a girl not be able to go to preschool because her mom is an alcoholic?

Successful people tend to see in themselves a simple narrative: You study hard, work long hours, obey the law and create your own good fortune. Well, yes. That often works fine in middle-class families.

But if you’re conceived by a teenage mom who drinks during pregnancy so that you’re born with fetal alcohol effects, the odds are overwhelmingly stacked against you from before birth. You’ll perhaps never get traction.

Likewise, if you’re born in a high-poverty neighborhood to a stressed-out single mom who doesn’t read to you and slaps you more than hugs you, you’ll face a huge handicap. One University of Minnesota study found that the kind of parenting a child receives in the first 3.5 years is a better predictor of high school graduation than I.Q.

All this helps explain why one of the strongest determinants of ending up poor is being born poor. As Warren Buffett puts it, our life outcomes often depend on the “ovarian lottery.” Sure, some people transcend their circumstances, but it’s callous for those born on second or third base to denounce the poor for failing to hit home runs.

John Rawls, the brilliant 20th-century philosopher, argued for a society that seems fair if we consider it from behind a “veil of ignorance” — meaning we don’t know whether we’ll be born to an investment banker or a teenage mom, in a leafy suburb or a gang-ridden inner city, healthy or disabled, smart or struggling, privileged or disadvantaged. That’s a shrewd analytical tool — and who among us would argue for food stamp cuts if we thought we might be among the hungry children?

As we celebrate Thanksgiving, let’s remember that the difference between being surrounded by a loving family or being homeless on the street is determined not just by our own level of virtue or self-discipline, but also by an inextricable mix of luck, biography, brain chemistry and genetics.