Black bears rarely attack. But here's the thing. Sometimes they do. All bears are agile, cunning and immensely strong, and they are always hungry. If they want to kill you and eat you, they can, and pretty much whenever they want. That doesn't happen often, but - and here is the absolutely salient point - once would be enough.
A Walk in the Woods: Rediscovering America on the Appalachian Trail (ed. Broadway Books, 2010) - ISBN: 9780307717832