That's a good way to look at it. I always try to log results the same day. In the past, I have not been as faithful about logging DNF's as I should have, but after reading the various threads on the forums, my new policy is going to be the same or similar as others:
1. Hit goto on the GPS,
2. Arrive at GZ,
3. Search for cache,
4. and then log results.. either smilie or DNF.
If for some reason I don't do 2 or 3, then I won't do 4.
I second that. Sometimes I may get close to GZ and find I am not attired appropriately or that I don't have the right equipment to go after it so I leave and mark it for another day. In these cases I do not usually log the DNF. When I do log a DNF (which I do if I actually searched for the cache for any reasonable period of time) I always give some detail in the log about how long I looked and any other important details so that other cachers who read the log can make an educated decision about whether to even try. The problem is that a lot of cachers won't even look for a cache that has one DNF. They don't look at the logs, they just use GSAK to filter them out. One DNF logged by someone who did not really even look for it can result in a very long period where people avoid the cache.