The conventional story is that the U.S. has undersaved and overconsumed for decades…
Why is that story wrong? It ignores the fact that households and institutions make up only about a third of U.S. gross saving.
Domestic businesses, which do the other two thirds of U.S. saving and are not reflected in that personal savings rate, have been saving far more than they have in the past. That has offset the decline in personal saving. We can see that in a graph of gross private saving over gross domestic income below.
The U.S. saves about one fifth of gross domestic income — it saved a little more than that in the 1970s and over the last few years, a little less than that in the 1950s and the 1990s. The apocalyptic trend towards zero savings is simply not there. What appears to be a long-term decline in the savings rate is in fact a hand-off between households and businesses in who does the saving.
There are useful graphs at the link and basically it means you should have bought those extra Christmas presents. I would add the cautionary note — for Americans but not for the world — that business savings may be more mobile internationally than are household savings. You also can view these numbers as a harbinger of greater wealth inequality in our future.