* No central tracking: There's no global database that tracks the sales of every single book published.
* Self-published books: A vast number of books are self-published, and their sales figures are often not publicly available.
* Defining "worst": "Worst selling" could be interpreted in various ways: fewest copies sold, lowest revenue, or even books that failed to recoup their publishing costs.
However, there are some examples of books that are widely considered to be commercial failures:
* "The Book of the SubGenius" by Ivan Stang is often cited as a book that sold very poorly. It was published by the SubGenius movement, a satirical religion, and is considered more of a cult classic than a commercial success.
* "The Complete Idiot's Guide to Microsoft Office" by Gary R. Davis was a commercially unsuccessful book despite being part of a popular series. It was likely overshadowed by the dominance of Microsoft Word and Excel as individual programs.
Ultimately, it's difficult to declare a single "worst selling" book due to the lack of comprehensive sales data and the varying interpretations of "worst."