He tripped. His logic was wrong. Cleverness failed. How could this happen?
Being the smartest person in the room used to be enough. It was pretty easy to attain the position; most people's brains were untrained mush. He was so confident of his superiority, he used it as a shield to deflect bullets and turn away knives and dodge blame. Nothing could harm him.
Then it happened. The knife slashed. The gun fired.
There was no dodging the blame but it no longer mattered. Lisbon was stabbed to death. He was paralyzed from the neck down. Red John ran free.