One important thing to remember: While American Whitewater has tried to systematize and standardize the whitewater ratings as much as possible, the numbers are still basically someone else's opinion, and that person most likely is a far more skilled paddler than you are. Another is that the ratings necessarily are based upon assumptions. They take for granted, for example, you'll be following behind an experienced paddler who's been through that particular rapid before and knows it well enough to give you some guidance.
They also assume that the rocks and tree trunks in the rapid are still in the same places as they were when the rapid was surveyed, which isn't always going to be the case, though the AW tries to keep its information up to date. They're based upon normal climate conditions for the time of year that the rapid is considered most runnable, so if you pick a different time of year, you're taking your chances [source: Belknap]. And perhaps most important: There's no way that the ratings can factor in the unpredictable. A heavy rain, a sunny winter day that melts some off the snow pack, or the release of an upstream dam can increase the speed and power of the water flow, significantly raising the difficulty level of a rapid [source: Safety Code of American Whitewater].
Also, keep in mind that the AW rating system is only one part of the safety regimen that all paddlers need to follow. AW's safety code, which you can find on the organization's Web site, provides a good working list of the preparations you should make, including wearing a life jacket and a solid, correctly fitted helmet, mastering techniques for escaping from an overturned craft, and familiarizing yourself with basic first aid and CPR. Finally, the AW counsels you to be honest with yourself. Resist pressure from your buddies, even if they call you a coward. Take a careful look at the rapid beforehand and decide if your skills are up to the task. If you're not comfortable with what you see, remember that there's always whitewater somewhere else on another day that'll be safer and just as much fun.