just checked using the GSAK macro on the challenge cache
and i Have 137 Dnfs that i have since found out of 577 logged DNFs
and as i have found 5029 caches that means i log a DNF every 10 caches........ ineptness maybe
Couldn't resist checking this out myself with the macro and my figures are not too far from yours. I have 132 DNF's that I have since found out of 364 logged DNF's. I've only found 3974 so I log a DNF around every 12 caches - somehow it feels a lot more.
I would be interested to know how many times I have been the first or only person to DNF a cache as I seem to have particular difficulty with ones other people find easy.