Remind yourself that the obstacle is the way*. The fact that you don’t want to write at this moment means that you should be writing. The fact that your mind calls on you to give up because your idea is a failure is the number one sign you should power through and change it until it becomes better—even if it means giving up on your original idea to pursue another. For what great creation has emerged without a struggle? What great man or woman had no obstacle to overcome? Instead of saying that you “have to” overcome the struggles of creativity, remind yourself that you “get to”. Few have this privilege. Don’t take that lightly.
*See Ryan Holiday’s The Obstacle Is the Way.