Is the national health insurance system of avoidable?

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I prefer not to join it as it is expensive. But I have read you are expected to pay for the past years when you join it. So would be wiser to join it now and start benefiting now if one will pay for these days sooner or later anyways. So my question is, did you have or hear situations where one had to join it mandatorily? Do you have any wise tips and tricks to avoid the joining?