The gratifications come from creatively solving problems produced by creating. This is true for all kinds of creative work, and here is how Flaubert explains it for his, writing:
I love my work with a love that is frenzied and perverted, as an ascetic loves the hair shirt that scratches his belly. Sometimes, when I am empty, when words don’t come, when I find I haven’t written a single sentence after scribbling whole pages, I collapse on my couch and lie there dazed, bogged in a swamp of despair, hating myself and blaming myself for this demented pride which makes me pant after a chimera. A quarter hour later everything changes; my heart is pounding with joy. Last Wednesday I had to get up and fetch my handkerchief; tears were streaming down my face. I had been moved by my own writing; the emotion I had conceived, the phrase that rendered it, and the satisfaction of having found the phrase—all were causing me to experience the most exquisite pleasure.
(Quoted from page 1 of First Person Singular: Writers on Their Craft, compiled by Joyce Carol Oates. Ontario Review Press, 1983.)
For a very brief biography of Gustave Flaubert, click here. For images of or relating to Gustave Flaubert, click here.