Writing a book is not the same as writing for a daily paper. It exercises completely different “muscles” in your brain (we hear) and takes a lot longer.

That may be why Bill Keller is still paying back an advance to Simon and Schuster for a book he never completed.

He never completed two, actually, he says in Sunday’s magazine.

In 2002, the NYT published an essay by writer Joseph Epstein that cited a survey saying 81 percent of Americans “feel they have a book in them.” Don’t believe it, Epstein said. “Why should so many people think they can write a book, especially at a time when so many people who actually do write books turn out not really to have a book in them — or at least not one that many other people can be made to care about?”

That apparently includes Keller. Editors are only human, after all.