There is a very refined system in place.

We look at the trail in front of us and say one of the following:

• "Looks easy enough to me..."
• "Hmmm, there are a couple of ruts/rocks I need to watch out for, this might be interesting..."
• "Damn! That's steep! There's a good chance I might break my a**/have to hike...oh well, here goes!!"
• *looks at friend* "Dude, there's no way I'm doing THAT! You're insane!"

It's very scientific and involves a lot of cataloging of data but, in the end, we have a highly technical classification system ready to roll!!