Christopher Nolan's 2020 sci-fi action thriller Tenet is a big heist-style movie in which the titular organization attempts to stop the end of the world through time travel. Due to the sensitivity of their mission, characters often repeat the phrase: "We live in a twilight world. There are no friends at dusk." While nominally, this phrase is used to identify whose side someone is on and, thereby, avoid divulging secrets to an enemy, one theory suggests this phrase might have another meaning.
A Reddit theory postulates that "twilight" and "dusk" could stand for hope and rebirth, with an unspoken "dawn" being despair and death, much like going into a white light. Therefore, when Protagonist (John David Washington) attempts suicide at the film's beginning, he is in the "dawn" and has his rebirth as a TENET agent. From there, he moves toward "dusk," which is represented by the end of the film and TENET stopping World War III.
The Meaning of 'We Live in a Twilight World' in Tenet
The "no friends" part of the phrase has to do with Neil (The Batman's Robert Pattinson), Protagonist's handler and guide. He moves in the opposite direction of Protagonist -- whom he guides as the "twilight" -- and eventually dies, having reached "dawn." Thus, over the course of the film, the two see ghosts of one another in changing the course of the future and preventing World War III.
As Neil dies when Protagonist is at "dusk," Washington's character is without his friend. In this case, the phrase signals an optimistic move forward for Protagonist and everyone else moving through the "twilight world," while Neil sacrifices himself in heading toward the "dawn." This is only one of several interpretations of the phrase.
The Multiple Meanings of Tenet's Phrase Reflects Christopher Nolan's Themes
Another thread suggests the inverse is actually true. In this alternate theory, the future from which Neil comes is dying, so by moving backward through time, he's moving away from despair and toward hope. Therefore, the Protagonist begins in hope and moves to despair near crunch-time, and Neil begins in despair and goes backward toward a better time.
Nolan's films frequently embrace ambiguity and allow for multiple interpretations. As such, much of the meaning of a phrase like "we live in a twilight world" depends on the direction from which one looks at it, and there may not be just one valid interpretation. Instead, there are a variety of potential meanings for "We live in a twilight world."