If you earn twice as much one month, you don't spent twice as much on rent, groceries, or commuting that month. You do spend more than twice as much on tax, probably should spend twice as much on savings and pension contributions, and probably will spend twice as much on living large.
So surely it's important to account for the marginal cost of spending money, but not operating expenses?
So surely it's important to account for the marginal cost of spending money, but not operating expenses?