You should first guess how many years you have left to live. Then estimate how many books you can read in that time. Then go to your book collection and sort the books in the order that you wish to read them (including those you have already read that you will read again) until you have equaled the number that you estimated you could read in your entire life. Then sell/give away all the other books. Then do not buy any books unless you come across a book you really want to read and only if you want to read it imminently.It struck me as a really bad idea or rather as the idea of someone who is not a reader. One of the things that makes reading interesting is that one book may stimulate new interests and lead you to the reading of other books. It is therefore difficult--I would say "impossible"--to predict what you are going to read next. It's the kind of advice someone would give who would ask "Have you read all these?" when entering your office. Someone with this view does not understand that books are, among other things, tools. Some tools are not used very often. Some tools, like reference books, for instance, are used frequently. And you never really know when a book will become a reference book for you.
On the other hand, there are (still) libraries. If I had to thin out my book collection--and I do--I would use a different criterion, namely how useful do you think a book will be for the rest of your life. Obviously, the person who wrote the quoted passage has no real use for any books.
1. See here.
2. See also Have You Read All These?.