The dramatic irony of the book
The book explores through dramatic irony what it felt like to not know that the Towers were going to be attacked and fall. For instance, there is a sporadic character named Hammad who ends up being a hijacker involved in the terrible Terrorist Attacks, but the reader doesn't see that until the end. This places the reader back into the role of someone who had not heard about the attacks before. Indeed, the work of the characters is to restore some kind of innocence about those attacks, but they are painfully within the domain of experience.
The survivor's guilt
Although there is nothing morally culpable in Keith's survival, he still exhibits a kind of agony for having survived a catastrophe that so many others did not survive. His survival was miraculous and important, but he continues living life in the dead-man's daze. He haunts the streets of New York, not inhabiting them. The irony of this guilt is that he didn't do anything wrong at all. The confusion is part of how terrorism harms a nation.
The failed marriage
In a metaphor for nostalgia, the paramedics drop Keith off at his ex-wife's apartment. This places him in a narrative from the past, but what is there to salvage? The marriage was already over when the attacks took place. This irony shows the painful irony inherent in intense feelings of nostalgia. The desires of nostalgia are desires for something from the past that wasn't even there. These feelings define post-9/11 America, because some innocence was lost that wasn't recoverable.
The ironic performer
It is incredibly ironic that a performer called "Falling Man," the titular image, would willingly recreate the horrific scene of innocent people jumping from the burning World Trade Center towers. What is more ironic still is that Lianne finds comfort in these recreations. The irony shows that the sight was horrific and blatantly traumatizing. By re-afflicting themselves with that vision, the man falling to his death, the people remember why they feel so damaged. It is a bizarre and ironic desire to revisit traumatic moments.
Keith's ironic career choice
When Keith takes up the profession of a friend who died in the attacks, he raises an interesting irony for consideration. He becomes a poker player. Where does the poker player live? The poker player lives in the world of the future, calculating odds, attempting to know what might happen in the future. This use of irony underlines an important change in Keith's character. He is now defined by his desire to see the future. He wants to know when traumatic things might happen in the future, but since that is impossible, he becomes a gambler who does something similar over a card table.
