"About 1 in 6 borrowers, or 3.6 million, were in default on $56 billion in student debt"

I thought "default" is technically impossible with respect to student loans, your solvency matters not, you're obligated to pay it off even if takes your entire life (and/or life's earnings)?

This problem would get fixed very quickly if students were allowed to actually default on the loan and stop paying it, at which point it becomes a loss to the lender, like it is with any other loan. Then these loans wouldn't be handed out like candy to people who are not mature enough to understand what it takes to pay off $100K and thereby ruining their lives.