It does not appear on a spreadsheet. It rarely comes up with an advisor. But it sits in the back of the mind of millions of people in their 50s: Eventually, there will be my parents’ house. Eventually, there will be whatever is left in their accounts. It will not solve everything. It will help.

I understand the instinct. I have spent a career building businesses around finance and how long people live, and this assumption turns up everywhere. It is seldom stated out loud. It is almost never stress-tested. And it is getting less reliable every year.

Start with the number everyone has heard. Something close to $124 trillion in American wealth is projected to change hands by 2048, and Gen X is first in line. About $14 trillion of it is expected to reach Gen X households over the next ten years. Set against a generation that saved a fraction of what the boomers had at the same age, that sounds like a rescue arriving.

It is not. Three things get in the way.

The average is a mirage