There’s a conundrum in President Biden’s relief plan for student loan debt. The more merciful the government is to debtors, the worse the incentives it creates. People will be more likely to borrow unwisely if they expect the government to forgive their unpayable loans.

This is an old problem for governments, of course, but it’s stark in Biden’s student loan relief plan, especially the income-driven repayment plank, which has gotten less attention than the forgiveness of up to $20,000 in federally held loans.