Houghton Mifflin Harcourt hasn’t said what it plans to do with all the copies of Imagine, Jonah Lehrer’s sullied best seller on the science of creativity, that it has yanked from shelves. But most book people agree that the copies will eventually be pulped, or dissolved into a milky liquid and reconstituted as clean paper. In this regard, at least, Imagine has plenty of company. Every year, millions of books are sent to the “cruel machines,” as one young editor calls them, simply because their sales didn’t meet projections. The process is tidily symmetrical: from the vat to the store and back to the vat.