I recently came across this quote from Martha Graham (which according to Wikiquote is from page 264 of Agnes de Mille’s The Life and Work of Martha Graham) and it’s been in my thoughts often since then (italics mine):
There is a vitality, a life force, an energy, a quickening that is translated through you into action, and because there is only one of you in all of time, this expression is unique. And if you block it, it will never exist through any other medium and it will be lost. The world will not have it. It is not your business to determine how good it is nor how valuable nor how it compares with other expressions. It is your business to keep it yours clearly and directly, to keep the channel open. You do not even have to believe in yourself or your work. You have to keep yourself open and aware to the urges that motivate you. Keep the channel open.
When impostor syndrome is railing at me about my art or my writing, the italicized portion is what comes to mind. I find it reassuring.