That was a comment I read some time ago coming from Umberto Eco. He has a very big library and he occasionally gets asked by visitors to his home if he read all or most of them? His answer was long your lines. Of course he had not read most of it at all - because what was the point of keeping a library mostly consisting of books you already read? Your library should be the exact opposite to be useful, i.e. mostly consisting of books you had not yet read. Unfortunately I forgot where I read that.