In reply to MG:
Probably like many others I was reasonably used to navigating in poor vis and at night. But I always chose to navigate to and from obvious features that were particularly obvious to such as, tops, cols, and ridges and so on.
On the assessment (PYB) I was asked to navigate to tiny micro features (Spot heights, tiny tarns that were dotted amongst tiny tops and other tarns, features you could not see until you were on top of them and that were only just noticeable on a map. Somewhat innocently I assumed I could do this without much reference to counting paces, or using timings, something else I'd avoided where possible in the hills. The assessor was quite good in that he chose spots which could only be located if you counted steps and/or timed yourself.
The navigation was over two days/nights in mostly thick mist and rain. It bucked my navigation up somewhat though, but didn't do my stress levels much good!