"what is the marginal private rate of return on capital? [..] it’s not unusual to find sources which suggest a number for the average return in the range of 15% [..], with the median estimate running at about 12%[.] Let’s instead cut it down to historic U.S. equity returns and say seven percent for the return at the margin. [..] most government fiscal policy works through well-known, fairly large contractors that at the margin have already well-established networks of capital and labor. [..] Even in more down times, fiscal policy doesn’t always target unemployed resources so well. That means a government project faces a seven percent hurdle rate. You may wish to up that for risk [..]. Let’s say that brings us up to a ten percent hurdle rate, and that’s being quite conservative. [..] So that’s a (hypothetical) hurdle rate of ten percent, not zero percent. Of course it’s not unusual for private companies to use hurdle rates of twenty or more for their investment decisions. There are further complications if the borrowing is financed by foreign finance capital. But there is still likely a real resource displacement in the home market as robots are shifted from one line of work to another. [..] if someone tells you zero percent is the correct hurdle rate for government infrastructure investment, they are wrong. Opportunity cost remains an underrated idea in economics."