Or, to put it another way, while it might have taken the writer three days to shape that description of the forest, and so had time to savor each carefully crafted image, the reader is going past at a 1,000 words a minute. Okay, maybe if you're Proust or James Joyce, readers will slow down for you, but, um, you're not. Not yet, anyway. So less is more. Out of the ten images you've come up with, pick the best one; prune the rest. This will usually make the scene—and your writing—leaner, tighter and so much better.
Same with metaphors, jokes, and even surplus characters. Had a manuscript across my desk yesterday where a writer used essentially the same line twice within three pages. It was funny and it built up the speaker's character, but you can't get a laugh out of the same punchline twice in three pages; one of them has to go. Later that same day, I was reading a another manuscript where the author introduced several characters, spent time describing them, building up their personalities, but then didn't actually have them do anything in the story. They were just sort of there...except for one character who sat out the entire story in the barn, and so wasn't even there. Maybe save the barn character for another story.... Just because you thought of an image, or a metaphor or a character, or a funny line doesn't mean you have to use it. Keep to the point, keep things moving forward, and restrict yourself to your very best material.