Good reasons not to buy health insurance

Today I spoke with a woman who said she did not have health insurance because she had family members who would pay for her treatment if she got sick, but those same family members would not pay for her insurance premium.  Unfortunately for the national insurance scheme, this sounds perfectly rational to me (at least from her perspective; not the family members').

Another unfortunately rational decision: not re-enrolling each year.  The way the scheme is implemented now, if you enroll once, but fail to re-enroll the next year, you get coverage immediately at any time by just paying the premiums you have missed.  Many people only re-enroll when they are sick, and the treatment cost is more than the missed premiums.  This makes perfect sense, so why would anyone do otherwise?  As long as people can do this, this poses a problem for the sustainability of the scheme-- if the only people who are enrolling and paying premiums are the people who are getting sick, the scheme will never be able to finance itself.