I guess one of the problems I have with completing a book arises from not having a clear image of any imaginary readers in the future.
In conversation I might have the ability to amuse most people for an hour or two. Some people will inevitably consider me stupid, boorish, arrogant, etc - but I have quite a lot of experience at 'tuning in' to a wide range of people, as teacher, street performer, hitch-hiker, public servant, etc.
Feedback from a listener might tell me to avoid (say) politics or football, religion or eating habits, fashion or beliefs, etc - but given that adaptability we could probably carry on an interesting exchange.
When writing I don't seem to have a clear view of the reader. I could aim it at one person (like a letter - those are the things we did before emails) but once I get past writing for one I seem to get very inhibited.
In real life I talk to people who never swear, and others who always do. My favourite mix probably remains not swearing as punctuation, but saving the occasional swear word to drop in for shock value, emphasis, or for laughs.
Similarly, my cynical approach to the media and public reaction to the Death of Lady Di(for example), or 9/11, might get me a punch on the nose in one situation, and a cheer from another. Nothing to do with feeling sorry for an individual human being, or for 3000 human beings, just saying out loud, or sharing, a sense of the hypocrisy of the media, or politicians, for instance.
In writing a book I don't want to avoid jokes that might only make my friends laugh, but get taken right out of context by some casual reader. As a minor celebrity (about F-List) I have that 'role model' responsibility for young people, so can hardly promote laziness, defend drug-taking, encourage anarchism, mention atheism as an obvious default position, etc without drawing comments from 'concerned parents'.
On the other hand (probably talking about an autobiography now) I can't really talk about how I got here without honesty about my opinions and approach to life - and some of my more exotic experiences. I don't want to offer a Disney version.
Chatting in a bar, or on a bus, I could tailor my anecdotes to suit you...editing on the fly. A book seems a really permanent object which can be held up in court...
I see this (like so many ideas) has bothered others:
The Imaginary Reader: the imaginary reader, the real reader, the happy reader