I came close to buying the updated (2014) edition of Mearsheimer's Tragedy of Great Power Politics today in a B&N where I happened to see it. It's the same as the orig. ed. except it has a concluding chapter arguing M's view, with which I disagree, that China is unlikely to "rise peacefully." My pb copy of the orig. ed. has fallen apart so I figured why not buy the updated one. But then I decided to buy two CDs for $4.99 each, plus the current (summer) issue of NYRB, and in light of that I decided I really couldn't afford and didn't need the Mearsheimer. What I can afford is a somewhat elastic concept, but it boils down to "why the @#! am I spending this &%!@# money?"
ETA: On similar grounds I ask myself why I flush $130 down the toilet every year to maintain my 'inactive' D.C. Bar membership. There's sort of an answer, albeit not a very good one, but it would be boring and take too long to go into.
ETA (again): TBA will be pleased to know there was a prominent small table in the B&N given over to WW1 bks, including handsome (and not inexpensive, of course) new matched pb eds. of Tuchman's Guns of August and The Proud Tower. They said on them "Barbara Tuchman's great war series," even though Proud Tower is about pre-war Europe. Random House is not dumb.