Using the word "insurance" to describe our current system for sharing health care expenses is very misleading. Other misapplied terms like "risk pooling" further obfuscate our system.
Insurance is the opposite of a lottery. In a lottery, I pay $1.10 for a 1/100 chance of winning $100. The odds are "fair" - I pay $1 for a 1/100 chance of winning, plus 5 cents to cover the lottery company's cost and another 5 cents for their profits. True insurance like car insurance, homeowners insurance, etc. work in a very similar way. I might pay $110 a year to insure my car because I have a 1/100 chance of incurring $10,000 of damage in any given year. Again, I have to pay $10 extra to cover the insurance company's costs and their profits, but the arrangement is "fair": if 100 people just like me (same car, same driving patterns, same location, etc.) bought the insurance, the total premiums paid would equal the damage to our cars, plus overhead. Note that car insurance companies make every effort possible to try to determine the exact probability that you specifically will get into an accident, and will charge you a premium that reflects your individual risk. The insurance company charges you according to your risk - we use them because we prefer the certainty of a small expense to a low probability of a big expense. The insurance company provides this service by pooling our specific risk across a large population with predictable expenses in aggregate.
Health "insurance" today has very little in common with real insurance. The total health care expenses of a 100 young healthy people come nowhere close to the premiums they will have paid. A young healthy persons premium reflects a very small amount of insurance (the probability that they will incur medical expenses that year above their deductible) plus a very large wealth transfer to folks who are older, less healthy and less wealthy. This "insurance" is just a tax by another name.