If assumed to be valid over the complete range of possible values,
Which is where this logic fails. The saying is usually constricted to the range of “a lot of money” to “way too fucking much money”, with money less than “a lot of money” not included. Therefore the derivative can be positive, negative, zero, or anything really. Also to be pedantic technically the derivative doesn’t need to exist for a positive Δmoney to yield a positive Δproblems.
Which is where this logic fails. The saying is usually constricted to the range of “a lot of money” to “way too fucking much money”, with money less than “a lot of money” not included. Therefore the derivative can be positive, negative, zero, or anything really. Also to be pedantic technically the derivative doesn’t need to exist for a positive Δmoney to yield a positive Δproblems.