Some such billslike those that were erroneously issued for Covid-19 vaccinescan perhaps be written down to clerical errors or other such mistakes. But even in these instances, patients must shepherd themselves through the labyrinthine customer service processes of their provider, insurer, or both in order to rectify the situation. (A point at which many people, caught in the confusing warren of health care administration, will simply surrender their money just to escape, which surely nets the health care industry not insignificant piles of cash in aggregate.)

At least some portion of unpaid medical debt almost certainly falls into the category dubbed “surprise medical bills,” defined as out-of-network care at in-network facilities that was significantly curtailed by legislation passed late last year. But if understood more colloquially, there are still countless ways to rack up “surprise medical bills” as an American patient: You can have a medical emergency out of state, misread fine print, botch a premium or enrollment deadline, take a ride in an ambulance, get confused about provider networks, require particular care from a specialist, have a coverage gap between jobs, bungle some prior authorization rule, fail to tack a partner or baby onto your plan, or a bajillion other reasons.

I’ve heard countless stories of sticker-shock-inducing, life-altering health care bills, and often it’s difficult to discern exactly what went wrong and why. Health care journalists spend entire careers delving into the specifics of singularly egregious individual incidents; the best-known in the field are the ones with a track record of getting providers and insurers to cancel outrageous charges. But when you zoom out from the health care billing misadventures that make headlines, the larger scene feels much more random: For patients lucky enough to be insured, sometimes care comes through the way it’s supposed to. And sometimes it doesn’t.