Over confidence and in particular the idea that we are special and will live a long life suggests the error is saving too much. Note that we also tend to think that our partner will be alive as well. My wife once asked me whether we were saving enough for "our" retirement. "Sure," I said, "don't forget one of us will probably die before the other and I'm not saving for your future husband." "Why," she replied with a sigh, "can't economists be more human?"