That's what's meant by efficiency, it's allocating it to the place that has the highest return on investment.
As you point out, in practice what's efficient is what can capture the highest return, not necessarily the highest return per se. If say investing in education had high returns society wide but those returns couldn't be captured, that's not an efficient use of private capital.
As you point out, in practice what's efficient is what can capture the highest return, not necessarily the highest return per se. If say investing in education had high returns society wide but those returns couldn't be captured, that's not an efficient use of private capital.