Hombre (my hubby) once sold health insurance for awhile and later on passed insurance exams to be an insurance agent first in Texas and then in Kansas. And we both have worked in the insurance industry in various aspects over our respective lifetimes so are pretty familiar with how it works.
Most agents will go over an insurance policy with a policy holder to explain what is and is not covered in an insurance policy, but that is pretty tedious and boring and most people don't want to take the time. So most don't really know the fine points about either their health insurance or their car and homeowners insurance.
For instance on homeowners insurance, almost all policies will pay for water damage due to rain/hail after a tornado or other high winds tear off part of your roof allowing in the elements. But if water that comes in the form of flash flood, ocean surge and such damages your home, your homeowners insurance almost always does not cover that. You also need flood insurance. You also likely need extra earthquake insurance if you live in a earthquake zone.
Our Advantage Plan Health Insurance covers routine doctors visits, most prescriptions (some will have copay) and there is usually a pretty hefty copay if we go to the emergency room or are admitted to the hospital. Things like ultrasounds and xrays are completely covered in our plan but there will be a hefty co-pay if you get an outpatient Ct scan or MRI. There is often help for those who cannot afford the high copays. Our dental insurance pays all of routine checkups, cleanings, xrays twice a year and pays part of extractions, filling, crowns, dentures etc. But it will not pay anything on implants.
Some experimental medicines are not covered at all.
However annoying the complicated coverages might be, they are fully explained in the handbook we are provided. It is not the fault of the healthcare provider if we wind up having a claim denied for something that is not covered in the plan.