There is a challenge based on "avenging" DNFs. Your personal statistics on geocaching.com will let you know how many DNFs you have logged. Then each cache will update to that golden smiley face when you actually avenge yourself and find it. I have completed a cache or two under the old challenge system that included this. It was actually fun going back to find the caches that I had to DNF before they were archived. Some of them were in high muggle zones so I had to "watch" the cache and then respond quickly when the cache owner replaced them.