Desire leads to the gratification of desire, which in turn leads to the repetition of the gratification. Repeated gratification in turn leads to the formation of an intensely pleasurable habit, one that persists even after the desire wanes and disappears, the very desire without whose gratification the habit wouldn't exist in the first place. Memories of pleasure conspire in the maintenance of habit.
The ancient rake, exhausted and infirm, is not up for another round of debauchery, but the memories haunt him, of pleasures past. The memories keep alive the habit after the desire has fled the decrepit body that refuses to serve any longer as an engine of pleasure.
And that puts me in mind of Schopenhauer's advice. "Abandon your vices before they abandon you."