'Film' Aragorn needed some tough-guy boost, as he's now a more relatable protagonist
I haven't yet pinned down who made these decisions, but based on my memories of the books, reading around the subject and this fandom page comparing film and book it clicked that the character in the book is quite different to the movie.
In the books, as the above linked page implies, Aragorn is a pillar of confidence and willpower, even Sauron fears him claiming the ring. In the books he has no need to tell the audience he's going to hunt orcs to imply this. Books can more easily stick to Show, don't tell - films sometimes need to spell it out.
As well as the limitations/differences between the two mediums, in the films, he's portrayed as much humbler. He bows, he has doubts... he's more relatable.
My theory is that this is all deliberate. In the books Frodo is unmistakably the protagonist, as it's his burden of the ring that drives the story forward. He's very relatable as a sort of 'everyman' character. Not a mysterious ranger or a wizard, or an immortal elf.
The protagonist is the person whose experiences drive the story. The novel revolves around them. Readers are usually more connected to them than any other character.
— Louise Harnby, What’s the difference between a viewpoint character and a protagonist?
In the books also, Aragorn's story is more certain - 'he has a singular destiny'.
Aragorn, who was the Heir of Isildur, had been raised in preparation for his role in the final struggle with Sauron. Such hope was placed in him that his name among the Elves had been Estel, which means 'hope' in their language. [...] the Elf-lords saw in him portend of the final end of the struggle whether to victory or to defeat.
— LotR Fandom, Tolkien vs. Jackson: Differences Between Story and Screenplay
Therefore it's not his experiences in the book that drive the story, and we aren't rooting for him.
It’s [the protagonist] who we root for as they attempt to find resolution.
— Louise Harnby, What’s the difference between a viewpoint character and a protagonist?
In the movies, he's given more conflict to resolve - now he's more relatable. He seemingly has to pick between his destiny and Arwen (not something seen in the books), and he lacks confidence walking the Paths of the Dead. He's making choices we can relate to.
Peter Jackson is definitely framing him as a protagonist in his movies; a role he doesn't quite fit in the books.
The way this new protagonist role is shown, through humbleness and a lack of confidence which he must overcome, comes at the cost of him fitting the trope of the 'tough guy' and 'implacable leader' that he has in the books.
How do you balance the two? You give Aragorn lines where he can show confidence, not about his overarching conflicts (his destiny, Sauron, Arwen etc) but from something more relatable.
In the screenplay, the line is given not long after Aragorn fails to save Boromir from the Uruk-hai and Lurtz:
Lurtz aims his bow at Boromir's heart... suddenly Aragorn
charges at him, smashing the Bow with his sword. They lock
into a deadly battle. Aragorn cuts Lurtz down and races
towards Boromir, who lies slumped against a tree...URUK-HAI
arrows sticking out of his chest. At least 20 dead URUK-HAI
lie heaped around Boromir. His horn lies at his feet...Cloven
in two.
This gives him a loss to recover from, a failing to make up for. More relatable conflict. It's also much more grounded than the high-concept issues that he struggles with over the film. The audience see him fail to save somebody, then they get to see how he reacts:
ARAGORN: I do not know what strength is in my
blood, but I swear to you... I will not
let the White City fall, nor your people
fail...
This line (which I have emphasised) really hammers home Aragorn's character in the films.
- He lacks confidence in 'the strength in his blood' this is symbolising his destiny. In the books he has no such doubt, and this lack of confidence is not as relatable
- His vow is seemingly made to honour Boromir and Minas Tirith; Aragon's motivation stemming from a place and a person is more relatable and grounded than his 'destiny'.
So one of our protagonists has 'failed', shown weakness and now has to accept the call to take a phrase from Campbell's "Hero's Journey"*.
The failure, and his response is a major pivot for the character in the movie:
ARAGORN: Frodo's fate is no longer in our hands.
GIMLI: Then it has all been in vain...the fellowship has failed.
ARAGORN: Not if we hold true to each other. We will not abandon Merry and Pippin to torment and death, not while we have strength left. Leave all that can be spared behind... We travel light.
Having just taken a narrative blow from orcs, what can he say to show the audience he's accepted the call to adventure ('leave all that can be spared'), will face this adversity, and be a 'hero'? What will drive home that he's not defeated ('not if we hold true to each other'), and that he intends to take the battle to ones who killed Boromir and took the Merry and Pippin ('while e have strength left'), fight back against the forces of darkness, all while remaining relatable?
"Let's hunt some orc."
Footnotes:
* Campbell's "Hero's Journey" is not a one size fits all framework, and doesn't do justice to many other stories. It's quite applicable to Lord of the Rings, but I only mention it with this footnote caveat.
