This is not only a nice quote by itself, but seems to be saying something deeper to me about productivity.

There's a difference in productivity for it's own sake, but being both productive in the send of time spent efficiently and productive in the sense of producing something of greater value with your time than you might have spent doing something else which was less valuable, but which might still have been time well spent.

Adler and Van Doren indicate that outlining the arguments and structure of a book on its endpapers is a better and higher measurement of one's ownership of a text compared to a bookplate which only indicates the lower level of "financial" ownership.