Marcel Proust, in a paragraph containing two really, really long sentences (below), discusses the power of non-productive writing habits in an interesting way. He describes the experience of confronting inner forces of avoidance that clearly have the upper hand over the writer’s will.
“If only I had been able to start writing! But, whatever the conditions in which I approached the task (as, too, alas, the undertakings not to touch alcohol, to go to bed early, to sleep, to keep fit), whether it was with enthusiasm, with method, with pleasure, in depriving myself of a walk, or postponing it and keeping it in reserve as a reward for industry, taking advantage of an hour of good health, utilising the inactivity forced on me by a day’s illness, what always emerged in the end from all my efforts was a virgin page, undefiled by any writing, ineluctable as that forced card which in certain tricks on invariably is made to draw, however carefully one may first have shuffled the pack. I was merely the instrument of habits of not working, of not going to bed, of not sleeping, which must somehow be realised at all costs; if I offered them no resistance, if I contented myself with the pretext they seized from the first opportunity that the day afforded them of acting as they chose, I escaped without serious harm, I slept for a few hours after all towards morning, I read a little, I did not over-exert myself; but if I attempted to thwart them, if I decided to go to bed early, to drink only water, to work, they grew restive, they adopted strong measures, they made me really ill, I was obliged to double my dose of alcohol, did not lie down in bed for two days and nights on end, could not even read, and I vowed that another time I would be more reasonable, that is to say less wise, like the victim of an assault who allows himself to be robbed for fear, should he offer resistance, of being murdered.”
(Marcel Proust, Guermantes Way, In Search of Lost Time, Vol III; trans. Moncrieff, Kilmarti, and Enright)
As this exerpt illustrates, it can be enormously frustrating and anxiety inducing to be unable to change your own behavior about writing. The inner forces that interfere are not trivial to contend with, and attempts to become more productive must be planned with this in mind. In general, a gradual approach toward establishing regular writing routines works best, as more ambitious plans stimulate too much resistance.
And perhaps it would be best to start with sentences that are a tad shorter than those that Proust favors.