Being caught out, unprepared, in bad weather.
A good quote from the above article rings true. “Most trails are not marked for winter use, so navigation can be challenging“. Even if you are experienced, a blanket of snow can make staying on trail a challenge. Make sure you have a good topo of the area, a map, a GPS, and the skills to use them. The $1 trail maps you buy at a trailhead, do not count. Large scale maps do not show land features, topography, etc. and can cause you to second guess your whereabouts like the interviewee said last week.
Resources:
Mytopo. Custom printed maps of your area: http://www.mytopo.com/
Nat Geo maps: I carry one of these because I cover such a large area: http://www.natgeomaps.com/trailsillustrated