To write ~
Start with an idea, ponder it awhile, flesh it out and approach it from different angles and perspectives. Try it on for size; you’ll know when it fits. Next (or more appropriately, throughout) add passion to the mix, modulated by the voice only you possess, the one that announces to all that this is who and what you are. Sift it, shake it up, sit on it awhile, revisit as needed. When it feels right (write?), begin.
If it has momentum, the task is a pleasant, satisfying chore. The words and thoughts and essence of your message will fly from your fingertips, the keyboard barely able to keep up. Success does not necessarily follow but if it is a joy and genuinely represents your soul, your very core, then that is its own reward.
Should, however, the completed effort require more than you were quickly and easily able to give but you stretched beyond what you thought you knew to be your limits, very likely then, the warm glow of achievement, of a job well done will honor what was extracted.
This, I believe, is why we write.