These problems were anticipated, at least to a certain extent, and the Affordable Care Act contains features that were intended to mitigate them. That is why Obamacare offers subsidies meant to make insurance less expensive for people on tight budgets, encouraging healthy people to buy insurance. The law says most people can buy only during a set time period, discouraging people from waiting to buy insurance until they are sick and absolutely need health care. It also contains the notorious “individual mandate,” which imposes a fee on those who can afford to buy insurance but fail to do so.

Those policies probably helped encourage healthy people to buy insurance, but many experts are now saying the incentives weren’t strong enough. Many insurance companies lost money, because they set their prices hoping for a lot of dieters and ended up with the football team. That is why we have been seeing headlines about prices going up. If the average Obamacare customer costs more than the companies anticipated, they won’t make the money they expected without charging more for insurance.

In addition, another kind of adverse selection problem may be plaguing the Obamacare marketplaces, and it is harder to fix. The companies say it is not just that consumers were generally sicker than expected, but also that insurance companies offering access to a wider variety of doctors and hospitals ended up with costlier patients. In other words, insurers with national brand names like Aetna and UnitedHealthcare appeared to be losing more money than lesser-known companies with a history of covering patients on Medicaid.

The restaurant analogy is useful here, too. Imagine two all-you-can-eat buffets. One offers iceberg lettuce, chicken wings and macaroni. Its competitor offers the usual fare, plus lobster, and it charges a bit more. Guess which buffet will attract lobster lovers?

Executives from Aetna and UnitedHealthcare charged more for their insurance products than competitors that excluded high-end specialists and hospitals. They may have attracted customers who preferred expensive institutions and doctors and planned to use them.

That sort of problem can get worse over time. As the companies increase prices to compensate for having sicker patients, fewer healthy people will buy the insurance.

There are policy levers to address this problem, too. Provisions in the law require insurance plans with healthier patients to pay competitors with sicker patients a fee, but getting the formula right is difficult. Currently, insurers on both sides are complaining. Plans with healthier patients say their competitors are just better at making patients look sick. And plans with sicker patients say the payments are too low and unpredictable to make a difference.

In the meantime, insurers are reacting in two ways that diverge from what the law’s authors hoped.

Some are giving up on the new Obamacare markets, deciding that they like the à la carte business better. Those that remain are increasingly clearing their menus of anything that looks like a luxury item. Obamacare was intended to offer a variety of insurance plans with different features, catering to different kinds of people with different needs. The remaining plans may be adequate for basic health care. But their offerings look more and more the same.