The White Flag AA meeting (pp. 347–348)
You are behind bars; you are in a cage and can see only bars in every direction. You are in the kind of a hell of a mess that either ends lives or turns them around. You are at a fork in the road that Boston AA calls your Bottom, though the term is misleading, because everybody here agrees it’s more like someplace very high and unsupported: you’re on the edge of something tall and leaning way out forward….
Context
The Bottom redefined against its own name: not someplace low but someplace high and unsupported — a ledge, a leaning-out — so that the book's word for terminal addicted despair is topologically a suicide posture. Every jumper in the novel stands on this spot, and the caged lead-in is the theme's encagement idiom again.