This is a good point raised also by Deming early on in one of his books. The cost of any investment is not just the money spent, but also the risk-free rate com

This is a good point raised also by Deming early on in one of his books. The cost of any investment is not just the money spent, but also the risk-free rate compounded on that money over the time the investment is in use. In periods when the risk-free rate is 2 %, that is what any investment costs you in addition to the principal, as Deming put it poetically, "every day, rain or shine, even on Sundays."