The usual proximate causes for pension scheme funding gaps are excessively optimistic assumptions about investment growth and mortality, coupled with underfundi

The usual proximate causes for pension scheme funding gaps are excessively optimistic assumptions about investment growth and mortality, coupled with underfunding. i.e. you assume your investments will growth faster than they do, and you assume people will die earlier than they do, then you don't even put in enough to fund the scheme based on your optimistic assumptions. In the US, state pension schemes tend to use more aggressive growth assumptions than private ones: the government holds private companies to strict standards, but does not impose them on itself.