To understand economics and quality of life, grasp MPC, or

If a single parent earns $2000 a month and spends it all on raising her child her MPC =1, or 100%.  Her MPS, or Marginal Propensity to Save , is zero .  In fact, she probably often has to borrow.

Of course, she only has to work harder to be successful .

A successful inheritee has $200,000 a month to spend .  Most months he only spends $100,000 .  His MPC is 0.5 , or 50% .

He often invests the other 100,000 in tax-free muni bonds or in the off island tax sheltered accounts.

His savvy use of money  helps make America great .