> You can buy your own insurance

Depending on where you live in the US, this can be more costly than it's worth (compared to group coverage).

With group coverage you are paying much more than you think. The cost to your employer could have been paid to you as wages. The best option for buying your own insurance is to buy the absolute minimum coverage with high deductible and HSA option. Then put money in the HSA and save on income taxes.

> The best option for buying your own insurance is to buy the absolute minimum coverage with high deductible and HSA option.

It's probably the highest expected return, but the greatest exposure to downside risk (conversely, buying the near maximum coverage HMO plan is probably the lowest average return, but least exposure to downside risk.)

So this is a stupid questions but, what's the importance of buying insurance? Is it mandatory or something? PS. I life in Australia

It is mandatory in the U.S. as of a few years ago. There is around a $2,000 annual fine if you don't purchase insurance.