What else could go wrong with Obamacare?

"Young invincibles" are key. They are the young and the healthy. If they don't purchase health insurance, the program is at risk.

If too many exchange consumers are older or unhealthy, then monthly premiums will likely skyrocket in 2015 and this could cause the exchanges to topple. If that occurs, one of the highest-profile parts of the law will be viewed as a failure.

This group is so key that President Barack Obama spoke in Boston on Wednesday, hoping to convince this constituency to be patient with the website's problems and keep trying sign up for coverage.

In fact, he is targeting most of his sales pitch to them.

In an interview with Fusion TV on Monday, Obama made a tough sell to younger Americans. He highlighted a new report released by the Health and Human Services Department that found 46% of people up to age 34 are eligible for a subsidy that could provide them with insurance for $50 a month.

"Less than your cellphone bill, less than your cable bill," Obama said. "And about 70% can get if for less than $100 a month."

"The law would not be judged a success if the exchanges fail," said Drew Altman, president and chief executive of the Kaiser Family Foundation, a private, non-profit health care research organization.

To pass this test, the administration figures roughly 40% of exchange consumers -- 2.7 million if the Congressional Budget Office's estimates are correct -- need to be between the ages of 18 and 35.

Younger and healthier premium pools will keep overall costs lower and ease the financial hit to the program when it does pay benefits.

While the President has said that "You can keep your health care plan" if you like it, that's not necessarily true.

Well, it might be true if you purchased your plan before 2010 and have a plan that has been "grandfathered" into the Affordable Care Act.

But the reality is that many Americans will see drastic changes.

That's because the law now mandates that insurance plans cover certain services. So regardless of which plan you choose, whether it's the low-cost, high-deductible bronze plan or the most expensive, low-deductible platinum plan, they all have to provide basic services. Those services include immunizations, ambulatory care, prenatal care, newborn care, mental health and substance abuse services.

A full list is here.

While Sebelius insisted that some people will keep their insurance, she said those who are seeing their plans canceled "will have consumer protections for the first time."

"For some people, the coverage they have today is going to be changed to cover the new requirements," Robert Zirkelbach, a spokesman for America's Health Insurance Plans, said.

While policies now offer greater coverage, it comes at a financial cost.

It depends on the state but costs could go up for consumers. The Kaiser Family Foundation wrote in February that unsubsidized premiums for individuals and families "will be somewhat higher under reform than they are today."

Kaiser said many reasons are to blame for higher monthly out-of-pocket costs, including higher quality coverage due to minimum coverage requirements, prohibition on preexisting conditions and caps on out-of-pocket costs.

In addition to higher premiums, plans, especially the lower cost bronze and silver plans, include high deductibles. For instance, in Washington, D.C., deductibles for a family of three run up to $12,000.

While high premiums might prohibit people from being able to afford the monthly cost, high deductibles mean some may not be able to afford getting sick.

An estimated 4.8 million low-income people are likely to fall into what is called the insurance "gap." They are the people who make too much to qualify for Medicaid in their state but too little to qualify for federal subsidies for the insurance marketplace.

That's because subsidies for health insurance are available for people who make 138% of the poverty level, or about $31,300 for a family of four.

To accommodate the individuals and families who don't make that much, the federal government is paying for states money to expand Medicaid, but 25 states opted to not take the federal government's money and not expand Medicaid.

So many wage-earners, including most workers who earn a minimum wage, make too much to qualify for Medicaid but are too poor to receive federal subsidies. Purchasing insurance without subsidies is likely to be cost prohibitive for most in this category.