Self insurance is only possible for a truly insurable risk, meaning a risk that is measurable enough in the aggregate to be able to accurately estimate the amount that needs to be set aside. For a risk to be insurable, it must have a few characteristics, one is essentially needs to involve a large number of similar risks, so that the aggregate risk can be measured according to the law of large numbers. The other quality of an insurable risk is that it must not be catastrophic. Any risk where the potential loss is so large that no one could afford to pay the appropriate premium is not insurable. An example is that earthquakes cannot be fully insured against because an earthquake can cause more damage than any insurer has in total assets, and the proper premium would be so high, very, very few consumers could afford it.