When an idea for a Heavenletter pops into my head -- usually it's a first sentence I hear and write down. I listen, and sentences keep coming. It's like an impulse I hear. It is on a level before words. I have to start "taking dictation" right then. The best I know is that that particular impulse doesn't come again.
I remember one time when a whole especially evocative Heavenletter was finished a moment before. It felt especially powerful. And, then, it was gone, disappeared. I don't know what happened, and I wasn't able to ever get it back.
At the time this happened, the Heavenletter was still clear in my mind, and I tried writing it down again. It didn't work. I was trying to make it happen. Trying doesn't work. Trying is not at the right level. So I believe that each Heavenletter is a Once-in-a-Lifetime Opportunity, and, as often in Life, the time is now. The momentum is now.