The penalty starts at $95 or 1 percent of an individual’s income, whichever is greater. That’s in 2014, when the mandate takes effect. By 2016, when it’s fully phased in, the penalty will be either $695 or 2.5 percent of income. That’s compared to the thousands of dollars a legally acceptable insurance policy would cost if you were to go out and buy one.

So when Roberts said from the bench that “it is indeed likely that many [more] Americans will choose to pay the IRS than buy insurance,” he might have been right.

And if the mandate doesn’t bring in enough young and healthy people, the danger is that the pre-existing condition coverage that’s also in the law — guaranteed coverage for people with health problems — would force insurers to raise their premiums to cover their costs.