Everyone knows health insurance is important, right? It's obvious: If you don't have health insurance because you can't afford it, you know you are risking racking up serious long-term medical bills should you become ill.

But this series is about ways you can harm your financial future when you may not even realize it. For this series, the health insurance warning is really about choosing the wrong plan.

The truth is that every plan is different. Some plans allow you to choose your doctor, others don't. Some have great prescription drug coverage, others limit your options quite severely. If you get seriously ill, you may have to fight with your insurance company to get the treatment you want from the best doctor around. If you violate the provisions of your plan -- say by seeing a specialist that isn't in your HMO -- you may have to foot the bill.

I realized how important the details of your health insurance plan after I had two hospital stays in the same 12 months (but not the same calendar year). I had a C-section and then, eight months later, my gallbladder removed. My insurance covers only 90% of hospital stays up to a certain cap. That 10% in my case meant more than $2,000 of extra bills I hadn't expected.

Don't miss the rest of our series on 15 Ways to Ruin Your Financial Future!

Personal finance expert Dan Solin explains more in this post about the different types of insurance and why it is important to pay attention to the fine print -- not just the co-pay and the monthly premium -- when choosing a plan.

When you're young and virile, health insurance can seem unimportant. Choose unwisely, though, and you can spend a lifetime paying for your mistake. Too little, and a neck injury can leave you broke for life. And don't forget the risk of buying too much -- that can sap money that could be invested, compounding for decades.