First of all: Stop thinking of it as a skill roll. In the original rules, there isn't even an adjustment for high intelligence or having a guide. You don't get lost because you are a failure as a human being; you get lost because of circumstances beyond anyone's control.
Second: It's mostly a matter of messing up your map. The clue is that there is a 1 in 6 chance of getting lost when starting in a river hex. How could you get lost following a river? You can't, but rivers aren't straight; the multiple twists and turns may confuse you about where you are on the map.
Nevertheless, I would definitely not apply the rule about getting lost to every travel situation. The rule is in a section about traveling through unmapped wilderness. It's not meant for following a road, or traveling n a known area. This is when I would roll:
- Unknown Territory: Always.
- Unknown Territory, Heading Towards Landmark: Only when landmark obscured.
- Known Territory With Guide: Only in unusual circumstances (caught in storm, evading savages.)
- Known Territory With Ranger: Never.
A ranger only counts if the terrain is the ranger's specialty (not every ranger is woodsy...) Rangers in their specialty terrain shift down the list to the next item, so a prairie ranger leading the party through unknown territory towards a visible mountain peak on the horizon will only roll to get lost when a blizzard strikes; even clouds obscuring the horizon won't thwart the ranger.
On the other hand, magic or a curse shifts up the list at least one item; a ranger at best can only eliminate mild magic.