Steve Pavlina explains that the method he'd been taught in school-- a highly structured writing process of organizing what to say before it's written-- tends to produce dull writing, but starting from enthusiasm results in articles which are a pleasure to write and are apt to be more fun and memorable to read.
Inspirational energy has a half life of about 24 hours. If I act on an idea immediately (or at least within the first few hours), I feel optimally motivated, and I can surf that wave of energy all the way to clicking “Publish.” If I sit on an idea for one day, I feel only half as inspired by it, and I have to paddle a lot more to get it done. If I sit on it for 2 days, the inspiration level has dropped by 75%, and for all practical purposes, the idea is dead. If I try to write it at that point, it feels like pulling teeth. It’s much better for me to let it go and wait for a fresh wave. There will always be another wave, so there’s no need to chase the ones I missed.
This looks like PJ Eby territory-- it's about the importance of pleasure as a motivator.
I used to have this problem a lot, and it still bugs me at times. However, I discovered I could get round it by writing a rough text riding the first wave of motivation. It needs to be in proper form, notes won't usually do.
I can then leave it for a while and get back to the text in 2-5 days, regaining about 75% of the original enthusiasm. An additional advantage is that this method of revisiting tends to produce more coherent texts, too.