Where Do You Get Your Ideas?

In FEVERED HILLS, I didn't hold back. My prose is dense, full of little details, just like I like it. But sometimes I worry. Was I too liberal with my ideas? Did I use them up too readily? What if I only get a certain number of good ones and then that's it?--All gone!--and I find myself parched in a wasteland of repetition, scribbling the same tired old lines over and over on the proverbial chalkboard like a schoolboy in hell for all eternity.

Upon sharing a particular idea I was proud of, my wife told me not to waste it, to not give it away to one of my little pet project. She wanted me to keep it and use it for something larger, for one of my novels.

That got me thinking: How should I use them? Do I need to be more careful? Which are the really good ones? How will I know? Sometimes I have an idea or image I think is brilliant and it ends up being folded into a piece of writing as little more than a passing observation or detail. I feel like once it's used, it's gone. Should I be worried?