When the irresistible urge to immediately order that new Discworld book meets the heartfelt desire to preserve the memory of Pratchett's genius* by denying the existence of any book after I Shall Wear Midnight.
* Based on the ever-stronger suspicion that the new volumes (Snuff onwards) are either partly or wholly ghost-written**
** The only thing worse than that*** is that the newer books were indeed written by Pratchett, which would just serve to underline the damage Alzheimer's has wreaked upon him.
*** I lie. The worst thing would be that the disease has not really affected his writing, and he's just lost steam after 40 books. Which is understandable, but I'd rather not accept it.