Here's a quotation from Anne Lamott's Bird by Bird that has been helpful to me:
few writers really know what they are doing until they've done it. Nor
do they go about their business feeling dewy and thrilled. They do not
type a few stiff warm-up sentences and then find themselves bounding
along like huskies across the snow."
The fact is that sometimes
I'm dewy and thrilled, and sometimes I type like a husky bounding across
the snow. Those moments fool me into thinking that now I've got
this thing all figured out; now and forever, enchanting words will pour
from my fingers! So when the dew dries up and my husky comes upon a
six-foot wall of ice, it catches me off guard. Every time. Did I learn nothing from Wile E. Coyote*?
And so I also find this quotation (also from Bird by Bird) encouraging:
"Almost all good writing begins with terrible first efforts."
*obligatory highbrow cultural reference