A map and compass are fairly useless in a forest - or a "green tunnel," if you will. You need to be able to see landmarks in order to orient the map. Sure, you can tell which direction you're going, but not where you are on the map. I attempted to use just a map and compass when I hiked the CDT, and got a GPS at the first outfitter in Colorado (I hiked north). I know how to use a map and compass, but they just aren't that useful unless you have good sight lines (ironically, just the map and compass would have been more useful in Colorado and Wyoming because of the incredible sight lines).
Haiku.