This challenge tries to test how widely read you are, looking at fiction and non-fiction in a variety of categories. To come up with this list, I looked at a wide variety of sources. Many of the books on this list appear on some of the classic "best of all time" book lists from sources such as Amazon, BBC, NPR, and Time. However, I also looked at lists of most influential books, award winners, bestsellers, and a list of guilty pleasures on Goodreads. I also looked at lists of "best of" or "must read" books in a variety of specific categories (e.g., sports, science fiction, poetry, business) as well. When choosing books from these lists, I tended to favor books that are more widely known within the category since this list covers so many types of books.
There are certainly a lot of worthy books that are not on this list, and plenty of room for debate over the books I chose, but I think this list is a good test for how broad your reading experience is.