Given that First Man is about Neil Armstrong and the first moon landing, there's a lot of information to work with. When it comes to the big facts of the story, people generally know what happened. But, in the film, there are a couple times Armstrong is shown totally alone, meaning no one, except Armstrong himself, could know what happened in those moments. Spoilers ahead. For instance, there is a scene in First Man where Armstrong leaves his daughter Karen's bracelet on the moon. There's no way of knowing if Armstrong really did this, but based on research, it definitely seems possible.
"The bracelet is conjecture thats not mine, it's Jim Hansen's," says Josh Singer, the film's screenwriter. Hansen is James R. Hansen, the author of First Man: The Life Of Neil A. Armstrong, on which the film is based. Karen, as the film shows, was Armstrong's daughter, who passed away due to a brain tumor when she was only two years old.
Singer continues, "Jim, after four years of researching Neil and two years intensely working with Neil and talking with June [Hoffman, Armstrong's sister] and Janet [Armstrong, his ex-wife] and everyone else, started to wonder, what he did over on the Little West crater." It's know that Armstrong had wandered over to the moon's Little West crater, but no one knows what he did there.
According to Singer, Hansen asked Armstrong for his manifest, which would have shown what he had with him on the mission, "and Neil said he lost it, which is very un-Neil." Hansen then had a conversation with Armstrong's sister, and asked if she thought he might have left something of Karen's behind. According to Singer, she responded, "Oh, I dearly hope so."
For Hansen, and later for Singer, the idea of Armstrong leaving a keepsake of Karen's adds up when it comes to the trajectory of Armstrong's personal life, and it also wouldn't have been the only thing he left. "It's partially because of Neil's emotional journey," Singer explains. "But also because this is something that's done pretty regularly ... The Apollo 11 astronauts, in fact, left a pouch with an Apollo 1 mission patch." When it came to adding this detail to the movie, Singer thought, "Good enough for Jim, good enough for June, good enough for me."
As for the specificity of the item, a small beaded bracelet, Singer notes that the memento would have had to be something that Armstrong still had after a house fire his family experienced after Karen's death. "Jim said something of Karen's," Singer says. "They lost a lot in the fire. They lost a lot of personal mementos, specifically personally mementos of Karen's, so it would have to be something that survived the fire."
We'll never know for sure if Armstrong left something of Karen's on the moon — and, if so, what it was — but especially when watching it in the movie, it's fascinating to think about the first person on the moon leaving something so human behind.