“But there are also, odd, offbeat, happy days when something does happen as you write and your characters take surprising turns, sometimes revealing themselves to you on the page in a manner other than you expected them to be. You discover that you know more about life and your characters than you thought you did. Such days are glorious…there is also the sense of a governing hand (not necessarily and altogether your own.”
If you want to write then write. Most of the time you feel that you cannot do it or what you write isn’t any good. All writers have days like this. If you persevere you do get days like Mailer describes, and writing is always worth it.
So do it.