if you have to be sure don’t write

I saw this quoted in an essay I read this weekend and I had to hunt down the poem:

I had hardly begun to read
I asked how can you ever be sure
that what you write is really
any good at all and he said you can’t

you can’t you can never be sure
you die without knowing
whether anything you wrote was any good
if you have to be sure don’t write

W. S. Merwin,
from “Berryman