It's simpler than you think....
Despite Tenet’s palindromic structure, Christopher Nolan’s eleventh film is less about the nature of time than it is about the identity of one man—not that Nolan makes it easy. The first half of Tenet is a classic Bond spy thriller, with The Protagonist (John David Washington) cast as a noble CIA agent chasing world-ending MacGuffins. The second half is a military sci-fi complete with a soldier-approved “temporal pincer” move saving the day.
Tenet plays a shell game with the viewer. The plot raises a lot of questions, most of which obscure its primary concern, which Nolan indulges only in the final moments of the film. That concern can be summed up in two questions.
Who is The Protagonist?
In the future, The Protagonist becomes the head of Tenet, an organization he created to keep time flowing in the right direction. That means that everyone in Tenet is actually working for him, including himself.
Why does Tenet recruit him, specifically?
Because The Protagonist knows that unless he starts Tenet, the world could fall into temporal anarchy, he sends Neil (Robert Pattinson) back in time to recruit his younger self.
That’s the paradox at the center of the film—The Protagonist has to join Tenet so that he can start Tenet. Beneath the inverted bullets, The Protagonist is part of the same I Am Who club as Rey and Luke Skywalker (minus the paradox).
Unfortunately, Tenet isn’t especially interested in answering the ton of other questions that it raises. As Clemence Poesy’s scientist tells The Protagonist, “don’t try to understand it. Feel it.” That seems to be Nolan’s advice to the viewer as well. There is, however, one additional question that needed answering for the I-am-who of it all to make sense. Happily, Nolan answered it.
Who, exactly, is Neil?
The ending of Tenet implies that The Protagonist recruited Neil at some point in the future and that their friendship has been long and meaningful. That’s why The Protagonist sends Neil back to recruit his younger self—because Neil knows precisely who he’ll become. (Bonus Paradox! Apparently, The Protagonist recruits Neil because Neil tells him to recruit his younger self in the past).
But…but what about everything else? The temporal pincer? The reverse entropy? The grandfather paradox? The oxygen masks? The…the…everything?!?
Yeah…that’s what makes Tenet frustrating for some and re-watchable for others. For every answer implied, another question pops up. The exception is how central The Protagonist’s identity is to Tenet’s mission because The Protagonist is (and becomes) Tenet. His identity explains the film’s ending. Paradoxically, it also explains the beginning, if only in hindsight.