To a lot of people, that doesn't mean a great deal. I've read plenty of blog posts on the topic and clearly many readers don't have any qualms about admitting that the book they have chosen just isn't for them. Some even have the courage to go for an arbitrary page limit so that if they aren't enjoying a book by, say, page 75, its time is up.
I, however, balk at the thought of starting a book and not finishing it. Usually, I'm the rational sort and tend to approach decisions in a logical way rather than an emotional one. Boring, I know! :) That all goes out of the window when it comes to the very specific issue of not finishing a book. It isn't for the more commonplace reasons: not wanting to give up on something once you've started it; not wanting to have spent your hard-earned cash on something that you haven't finished; difficulty with the subject matter etc.
No, my problem is this: what if the book is going to become great just after I stop reading?
So that is where I stop being a rational person. It hasn't been great for the first 'x' pages - what on earth do I think is going to change in the last 100?!
My thoughts on the book in question have run something like this:
Pages 1-50: 'Am I enjoying this...? I'm not sure...well, I've only read 'x' pages so I guess it's too early to tell!
Pages 51-100: 'I just can't seem to foc - ooh! Look at the little ducklings -*Ahem* Right, focu...hey! Is my phone ringing?! Nope...' [Repeat with other cute animals or phantom phone alerts/email checks etc.]
Pages 101-150: 'I'm not sure this is improving...how many pages are there left? *Spends a good few minutes doing weird percentage calculations on mobile phone* Ok, so nearly half way, might as well make it to that!'
And now I'm at pages 200+ and I'm actually finding the book has improved a little. I suppose in some way, I'm hoping that the end will be so great that all the time I've put in so far won't turn out to be wasted!
But has it been worth all of the effort it has taken to get to this point? And am I the only person in the world who over-analyses such an objectively small thing as putting aside an unfinished book?! I can hear you all screaming 'If it's bothering you so much, just put it down and call it a day!'
NB: It is only fair to let you all know that this will more likely than not be a pontification that stays with me right up until the last page because, in the end, I'm just not sure I have the conviction for a 'DNF' in me...and that's just sad!