[jandrewrogers]

That 37% makes sense in that is roughly the percentage of the population where ordinary expenditures match income (per BLS). This has some elasticity though, since the scope of "ordinary" is much larger than "necessary" e.g. spending on luxury cars, food, clothes, etc is included as an ordinary expense even if it is profligate, so there is a latent surplus that is available and people do adjust their ordinary spending when necessary.

Per another Federal Reserve study I saw, the percentage of the population where income does not exceed necessary expenditures -- people with no income surplus, latent or otherwise -- is something like 12%. Which sounds about right and is still a lot of people.