Timing can be so important. It mystifies me how a particular moment is simply the right moment for specific poem to come together. I've had a few encounters with this sort of thing. And as thought I almost lack gratitude from the ones that have occurred this way, I'd add too damn few.
Some of the best poems can be viewed in the same way as a snapshot. They capture a moment in time and frame it in words. A yardstick to measure the success of such work could well be if the reader can put him/herself into that frame and automatically be in the moment. I think William Carlos Williams' poem that begins... so much depends upon a red wheel barrow glazed with rain is a classic example of what I mean. This poem came to him on the spot and indeed captures a moment in time like that of a photographer. Wickpedia notes "The pictorial style in which the poem is written owes much to the photographs of Alfred Stieglitz and the precisionist style of Charles Sheeler."
I'm trying to think about the few times I have had such an experience with writing a poem and it seems clear to me that there was little if anything I did consciously to assure the success of the poem written. I cannot think of any. In fact, these instances were more like becoming aware that there was nothing to do but sit down and write the poems. The conditions and the creation of the poem in these instances had more control over me than I over them. Because of this it is not something I can say, "ah, do this, and a great poem is bound to happen." Randall Jarrell ruefully defined a poet as someone who, in a lifetime of standing out in thunderstorms, manages to get hit by lightning seven or eight times.[The Atlantic.com] Perhaps these are lightening experiences.