Mountain biking often brings you closer to the wilderness than other forms of cycling, literally putting you smack dab in the middle of it all.
However, just because you are away from the cars doesn't mean you are completely safe. Aside from the abundance of wild animals, terrain may be even more of a threat to your safety.
Walking along the edge of a cliff face would be nerve racking for most, but how about riding a bike along it? How much do you trust your bike handling skills?