On writing my response I realized school was probably the one time where this sort of strategy would be appropriate for an individual. At the same time, school

On writing my response I realized school was probably the one time where this sort of strategy would be appropriate for an individual. At the same time, school is a much higher risk proposition (in many cases) and involves much more time and debt than the 40% guideline accounts for. You also have to keep in mind that most people who finish law school don't get big law jobs that allow them to pay off loans quickly. The same holds true for MBAs and most PhDs. About the only advanced degree that has some level of income guarantee (for now) is a MD. So while school can fit the 40% rule, it rarely does.