When the Democratic presidential candidate Elizabeth Warren put forth a sweeping plan to cancel student debt last week, she also exposed the deep divide between how liberals and conservatives think—and, inadvertently, why liberals often have so much trouble getting their ideas enacted into law.

Under the plan that Warren announced, about 42 million Americans would have up to $50,000 in outstanding debts canceled. Philip Klein, the executive editor of the conservative Washington Examiner, quickly chimed in with a tweet and a blog post criticizing the senator’s proposal as unfair.

New post: "Elizabeth Warren's plan to cancel student loan debt would be a slap in the face to all those who struggled to pay off their loans" https://t.co/4g6No2MRVm — Philip Klein (@philipaklein) April 22, 2019

Taken aback that Klein would cast his objection to Warren’s plan as a matter of justice, the Twitter left erupted with outrage and mockery.

Things were worse for people in the past so it would be unfair to make them better for people in the future is not an argument that makes sense if you think about it for more than a second. — Ezra Klein (@ezraklein) April 22, 2019

Child labor regulations a slap in the face to children who worked in coal mines https://t.co/llwzoNn1zB — Osita Nwanevu (@OsitaNwanevu) April 22, 2019

Personally, I understand the feelings that Klein’s post brought forth. I too am a liberal who believes that it is unconscionable to plunge 20-year-olds deeply into debt merely for wanting to educate themselves. More broadly, I favor many of the policy ideas that Warren has been rolling out. As an American-born psychology professor now living in Canada, I am a strong supporter of my adopted country’s universal health system, which has served my family admirably.

Read: The mental and physical toll of student loans

Yet because I’ve also spent the past few years studying how perceptions of unfairness differ for liberals and conservatives, Klein’s language didn’t surprise me in the least. There is more than one way to decide who is deserving of what.

One is by need: Some people have more than they need, and others need more than they have. Even when liberal leaders describe policies that are beneficial to everyone, they make it clear that the most important beneficiaries are those whose needs are most urgent. Indeed, Warren’s plan was also criticized from the left for insufficiently prioritizing those who need debt relief the most.

Still, there are other ways of judging what’s fair. Conservatives tend to value equity, or proportionality, and they see unfairness when people are asked to contribute more than they should expect to receive in return, or when people receive more than they contribute. Consider a hypothetical comparison of two people who graduated from college five years ago with equal amounts of debt. Jessie successfully implemented a plan to pay off the debt in five years, while Sam still has much to repay. Warren’s plan forgives Sam’s debt, but offers nothing to Jessie, despite her industriousness and self-discipline. To add insult to injury, Jessie must contribute tax dollars to the $640 billion fund necessary to forgive outstanding loans, including Sam’s.