When you publish a book, you need an ISBN number. One number is $125, if you buy ten they are $25 each, but if you buy 100, they are only $5.75 each. When I placed my order for an ISBN while finishing up the The Painter’s Workbook, I pictured myself writing so many books that I came ridiculously close to ordering 100 ISBNs. At the last minute, I came to my senses and only bought 10–“only” 10. Now having actually completed the book, I appreciate the true scope of such an endeavor, and I still have nine more ISBNs to go!