I would restructure the paragraph, because "forgettability" isn't a true attribute of the book; it is only a subjective perspective. If you're arguing that the book is forgettable (and giving reasons why), you're defending the hypothesis that a significant number of readers are likely to forget the content shortly after having read it.
Therefore, why not express it directly.
I suspect that readers are likely to forget this book soon after having read it, for the following reasons ..
But, oops, when it is worded this way, there comes to light the a glaring problem with defending the hypothesis: you're claiming that the book is forgettable, yet you're about to base an argument on the book's content, whose structure you must remember at least coarsely to be able to discuss it.
Thus, you haven't forgotten the book; but you expect that you soon will, as will others who read it.
The only way to write this is:
I suspect that readers are likely to forget this book because ... oh dear, I just lost my train of thought. Something about an incredibly boring, dull book? But what book? Never mind.