The two determinants of the importance of forgone earnings are the
amount of time used per dollar of goods and the cost per unit of time.
Reading a book, taking a haircut or commuting use more time per dollar
of goods than eating dinner, frequenting a night-club or sending children to
private summer camps. Other things the same, forgone earnings would
be more important for the former set of commodities than the latter.
The importance of forgone earnings would be determined solely by time