Well if the ornery bugs/birds/critters would just pay attention to my posing instructions, then I'd be making massively staged wildlife shots....
Doesn't look like that is going to happen, so I take what I can get. I think it helps to have an image in mind of what I want to capture and get in a good position to capture it, but then that is where the plan meets reality and plan B often gets called up...
That being said, there is often a good bit of making after the taking if the image you had in mind stretches the limits of the gear you have. I often wind up underexposing by one stop to get sufficient shutter speed and depth of field on many macro shots and have to adjust the raw file to get it back to looking like a daylight shot, then often a bit more tweaking to get it to look like what I saw.