The emotions he’s feeling when he’s retelling the story also infect the original memory. The NBC videos of the downed Chinook that he’s viewed repeatedly are dredged up as well.

Clever studies tell us just how powerfully words and images can manipulate memory to the point of inserting false memories. In one, researchers interviewed the parents of their experimental subjects, all college students, and collected true stories about events each of the studies had experienced.

After presenting these true stories mixed with false ones, researchers were able to trick 25% of the perfectly healthy students into thinking they had experienced one of the false stories just by having had them imagine any connections they might have to what they couldn’t remember. Brian Williams had plenty of connection to the downed helicopter.