Book!Crowley is Cool, but he’s also so so afraid and so stressed and so nervous all the time, and that’s actually what makes him so Cool.
I keep coming back to glibly describing the Ineffable Husbands’ arcs in the book as something along the lines of“Aziraphale gave up on an Eternal Heaven for interesting books and fine wine, Crowley faced Hell’s Wrath for good food and long naps”. The exact Earthly Delights aren’t important, there’s plenty of intersection anyways, but their relation to their respective sides is.
Book Aziraphale’s arc is about disconnecting himself from Heaven ideologically. He was already somewhat jaded about Heaven and aware that they’re Not So Different from Hell in some areas (“You'll be amazed at the kind of things they can do to you, down there.” ”I imagine they're very similar to the sort of things they can do to one up there.”) and disobeying his side obviously cannot be easy or safe for him - but the thing that's most important to his arc is that he did still keep insisting Heaven is fundamentally Good on some level, that Heaven’s victory in the Final Battle is assured and it’ll bring about a better world.
But for the sake of his individual hedonistic pleasures, he started working against this abstract ideas of a 'better world' and Heaven's ideas of 'goodness'. Because what's the point of an ideal world if it has no sushi restaurants or CDs? Gradually also getting more rebellious and morally disillusioned with his 'Side' and doing more 'unheavenly' and morally-gray things, until he was disparaging Heaven openly through the mouth of a preacher and passive-aggressively challenging the Metatron's authority at the Airfield.
And Crowley... well, the difference here was clear from the Beginning.
Aziraphale's worries about doing 'the wrong thing' seem to be mostly about... how he wants to make the right decisions because the right decisions are good. I'm sure he's got more practical worries about disobeying orders, but the focus is on the internal conflict between Heaven's orders and his personal sense of morality. Crowley however... doesn't want to have done the 'right thing', because it can get him into troubles.
Crowley always knew he’s working for ‘the Bad Guys’. He’s not totally ideologically disconnected from Hell either (‘“But it nearly worked," snapped Crowley, feeling he should stick up for the old firm.’) but he’s fully aware of what it means to be a Demon working for Hell tempting people into Evil deeds so that their Souls can be sent to Eternal Damnation. And he's got layers upon layers of rationalization and justifications for it, and he has found genuine passion and pride in his unique modernized form of sin-spreading that feels more mischievous than outright harmful, but underneath it all, Crowley just knows he's gotta keep pleasing Hell, or else.
His cool, confident, laid-back attitude is not exactly a façade, but it serves for a good counterbalance to what happens whenever he has to interact with his higher-ups (lower-ups?). Where even if he tries to still play it up like he's Cool Guy Crowley and he's totally chill and smug with higher-raking Demons, like Hastur and Ligur, the moment they break away from the area he feels is 'safe' (his MO as a tempter, in which he already proven himself to the Management) and shift to the End of Days, he clamps up and becomes nervous and 'haunted'. The narration, when describing his POV, sometimes tries to underplay it as just annoyance or frustration, the way that it tries to underplay his guilt in meddling in the affairs of Humans before the M25 and Adam plop that guilt right in front of his face, the way it tries to underplay his relationship with Aziraphale as a reluctant Arrangement of convenience despite all evidence to the contrary, but…
But Crowley’s fears about Hell are the most overt, probably because, well, his entire part of the plot is about being forced to accomplish a Very Important Task for his bosses (unlike Aziraphale, who until his ‘summons’ to the Final Battle, was perusing a personal side-quest no one in Heaven gave a shit about), and so they’re pretty much always breathing down his neck.
That’s what this whole ‘a Demon can’t have Free Will’ thing is really about. It’s less about him being Ontologically Evil, and more about, well, the Cold War Spy metaphor, he’s forever stuck in a shitty morally-compromising job, that despite all of the perks that allow him to live his affluent and effortlessly cool life, he could not leave, escape, disobey or fail at without suffering horrible horrible consequences.
But when faced with the prospect of losing Earth, and all of the experiences that come from living on it, even the most basic ones like a long sleep after a heavy meal, he tries anyway. He knows the consequences, he feels helpless and terrified, but he still risks Hell’s Wrath for food and naps.
...Well, his first plan is one that he convinced himself is relatively ‘safe’. An underhanded, cowardly trick worthy of one of Hell’s best tempters, but also informed by his very Earthly understanding of how the world works. If he performs his job as the Antichrist’s ‘Godfather’ as exemplary as he’s expected to, but places Aziraphale in to ‘thwart’ him then Armageddon could fail without Hell being able to place the blame on him. Probably. Hopefully.
And when it all falls apart and Hell does start coming for him. Well, first of all, it’s important that it’s in the same sequence that introduces us to Crowley’s idea of indoor gardening, which within the context of the book is absolutely him venting what he feels about the way Hell treats him…
And Crowley keeping that thermos of Holy Water in his flat shows that he’s been clearly paranoid of something like that happening for a while now. It’s a fear that’s been growing for longer than just the eleven years of the plot. And now it’s coming true. And Crowley has no choice but to face it. And he succeeds. Like, that’s part of what’s important about...
Crowley was outnumbered against two more powerful Demons. He was scared and he was underpowered and he faced one of his constant nightmare scenarios and he won. He outsmarted these two technically-more-powerful Demons with a little bit of foresight and a goofy pop-culture reference and a clever use of his natural Demonic abilities but mostly his natural (and very Human) cunning and knowledge of then-modern technology and his ability to play it cool even when he is scared and then he WON.
And from here on out, his road to Tadfield, to trying to stop the Apocalypse openly and directly, is basically him doing increasingly brazen and brave things, increasingly facing even more of his fears now that he's already got Hell pissed and after him. First trying to find Aziraphale at the burning Bookshop (clearly not as dangerous to him as it would be to a normal Human, but I won't say there was no risk of Discoporation), and then resigning himself to sacrificing the Bentley, and then crossing through the M25...
Like, the reason why this famous quote is so important...
Is because Crowley's optimism is truly 'underneath it all'. It's absolutely not self-evident. His inner monologue is always full of anxiety and fears and worst-case scenarios leaking through, thinking about how he can do nothing to stop Armageddon, thinking about how screwed he'd be if Hell finds out he fucked up Armageddon, thinking about how screwed up he is now that Hell found out that he fucked up Armageddon. One of the lines proceeding this one is literally "All was black, gloomy and awful. There was no light at the end of the tunnel-or if there was, it was an oncoming train." For the most part he might seem like a total pessimist, but he just... keeps going. He's cynical (that's his job!) and he's terrified and he just keeps going!
It's, y'know, layers. On the surface Crowley is this confident, laid-back and cool Demon that loves excitement and is costing through life not worried about anything, traffic cops chasing him around for speeding is just good fun so he can dunk on them. Below that, he's stressed out and scared, fretting about what will happen to him if he falls out of relative favor in Hell. But below even that, he is an optimist. A confident and utterly cool optimist.
And then he makes it to the Airfield, in the coolest way he possibly could, and... like, there are so many little character moments during the Airfield Climax. His insistence, with 'fatalistic gloom' that Adam stopping Armageddon wouldn't make a difference, but then his glee when he realizes that Aziraphale had found an out and joining him, even though it's clear how afraid he is of Beelzebub and that he is pissed with him... And then Satan comes.
Aziraphale's decision to stay and fight Satan is about his ideological disillusionment arc. Sure, fighting Satan might technically seem Angelic, but he makes it clear that he does it to 'make up' for all the troubles he caused Humanity as a representative of Heaven, explictly putting his 'Job' and Crowley's 'Job' as equally problematic, with no attempt to make himself morally superior. But for Crowley, when Aziraphale asks him to stay and help him fight, Crowley realizes that with all of his greatest fears already realized, all of his worst-case-scenarios having already come true, with nothing more to lose (well, I suppose he's still got Aziraphale to lose, but since the Angel already made up his mind to try and fight the Adversary, it's not like Crowley can do anything to stop that)... He is actually 'free' now.
Crowley realizes that deep down, he can and he wants to do such a brave and selfless thing.
Well, at the end, he doesn’t actually need to, but, like, it’s the thought that counts, right?
I think there’s a tendency in Fandom to treat characters with a seemingly self-contradictory nature as either just one side of their character or the other. Either flattened to their surface-level characterization or people do notice their hidden depths, but treat everything around it as a false facade and not another essential element of their character (this happens to poor Book Aziraphale as well). Book Crowley isn’t just the laid-back, confident demon he seems on the surface, or just a terrified nervous wreck pretending to be cool and confident, he is both. His ‘Cool’ attitude helps him cope with his fears and he is so utterly, utterly Cool not despite of, but because he’s so afraid.
