We live in a literary environment that – a little uneasily, I often think – feels the need to justify the reading and study of imaginative literature. That is understandable, for writers and readers often have to stand up and fight for what they care passionately about. We believe it is good for us, it must be good for us, this force we attribute to the enterprise of reading and writing. A wide exposure to great literature, it is claimed, provides a basis upon which we may feel more deeply, understand more widely, become better.

If this is an empirical proposition, I rather doubt it, though I have no substantial evidence for my scepticism. I have not interviewed thousands of teachers, novelists and critics in order to quantify their goodness on some objective scale. Horrible thought. So I rely, here, on some degree of self-examination. I am pickled in the brine of literature, as an academic, critic, and writer. I have read pretty carefully and widely for 50 years. If there is something enhancing about such an exposure, I should be showing some signs of it by now.

Sometimes, for sure, I can feel the old Leavisite values kicking in, and am able to consult an inward panel of fine sensibilities, and to employ those voices in making my own judgments. The question "what would Jesus do?" is not entirely inane, and if you substitute Montaigne for Jesus, you have a useful tool at your disposal. (Not that he would do much, but he might have a lot to say.) But for every such benefit there has been, I am sure, a corresponding loss, as there must be in a class of persons who so widely, and often unreflectively, introject the voices of others, and psychically identify with those wiser than themselves. Jung calls this process psychic inflation, and you can see examples of it everywhere in literary life. I try to guard against it, but it recurs, like bouts of malaria.

I wonder, too, if this insistence on the improving qualities of our baptismal dips into the waters of literature does not blind us to the real thrill of reading; the recurrent reason why we come back for more, remember, quote, argue, share our experience of books? For me, reading needs to be justified not in terms of some notional moral benefit but – that more dangerous and enticing category – pleasure. I read because I love to read, because, in the company of a book, I am happy, engaged, and inexorable. This may well be bad for me, as selfish pursuits often are: taking me out of contact with my nearest and dearest, making me shirk obligations from washing up to keeping up. "I am reading! Leave me alone!" is the mantra of every true reader.

So reading is an uncertain basis for the building of character. I am less ambivalent about writing. My writing, anyway. It has become increasingly clear to me over these last 10 years, in which I have written more regularly than before, that the more I write the worse I become. More self-absorbed, less sensitive to the needs of others, less flexible, more determined to say what I have to say, when I want and how I want, if I could only be left alone to figure it out.

Alan Hollinghurst has recently observed a similar phenomenon in himself, and used it to explain why he lives alone. "I'm not at all easy to live with," he says. "I wish I could integrate writing into ordinary social life, but I don't seem to be able to. I could when I started. I suppose I had more energy then. Now I have to isolate myself for long periods."

You don't, of course, need to live by yourself to become isolated. When I am writing I wander in a fug all day, wake in the middle of the night – waking my wife Belinda as well – and stagger downstairs to record a thought or two. Leave the bed with my mind whirling with gorgeously formed sentences which are as evanescent as the smell of lily of the valley, and about as easy to recall. By the time I get to the keyboard their perfection (as it seems to me in my drowsy creative mode) has dissipated, and though I can catch something of what seemed a sensational formulation it is already, in that Platonic way, only an imitation of the ideal. I fiddle about, rewrite and reconsider, and go back to bed an hour later thoroughly stimulated, dissatisfied, and unable to sleep. I read for another hour. The next day I complain that I am tired, and show all the signs of it: irritability, abstraction, and a tendency to fall asleep on a sofa at any time, including when I am being spoken to.

There is nothing unambiguously agreeable about this to my loved ones, nor to me either. It is embarrassing, being thus conquered by an inward voice desperate to formulate, reconsider, construct, deconstruct, seek out the right phrase, amend it, think again. And I am only a writer of bits of non-fiction. You'd think it would be easy. Or easier, certainly, than being a novelist. I can hardly imagine what it must be like to be inhabited by many competing voices, ceaselessly reconsidering the flow of a narrative, charting the development of character, juxtaposing one thing with another. It's astonishing that novelists have any social life at all.

But they do, of course, many of them with apparent success. Perhaps they do not suffer from open tap syndrome, and can shut off the flow whenever they like? Lucky them.

I console myself (and Belinda) with two thoughts. First, I am not writing all the time, and can be quite good company when I am not. And second, though I pay a price for it, writing – or more accurately having written – makes me happier than I have ever been. If the process of composition is laborious, antisocial and abrading, the moment when the first copy of a book arrives, or an article appears in print, is great. Not unalloyedly, because even when I read what I have published I keep rewriting it in my head. Bad transition here, clumsy phrase there, something that could have been left out, or put in. The work is never finished, not when I re-encounter it.

I consequently have a lot of trouble letting a piece of work go, pushing the send button that irrevocably passes a manuscript into the hands of an editor, and ultimately a reader. I mentioned all of this to my old friend the publisher Tom Rosenthal, complaining about my compulsive revising of my own work. I thought he would understand, having published a lot of writers considerably fussier (and better) than me. But he wasn't remotely sympathetic.

"That's not writing, that's wanking," he said censoriously. "Finish it, and get on with something else!"

It was good advice, and one day I am going to follow it.