Wow, that's a lot of information all in one table! There are other issues here as well, such as duplication of data (often referred to as 'redundancy'). For each book that a user checks out, we have to repeat all of the user data in our table. It's a similar story with the book data, if more than one person checks out a book, such as with 'My Second SQL Book', we have to repeat the book title, author, isbn, and published date.
what if for one of the 'My Second SQL Book' checkouts the title is entered as 'My 2nd SQL Book' instead, or a typo had been made with the isbn on one of the rows? From looking at the data in the table, how would we know which piece of data is correct?
How do we deal with this situation? The answer is to split our data up across multiple different tables, and create relationships between them. The process of splitting up data in this way to remove duplication and improve data integrity is known as normalization.