Rowan of Rin

A book by Emily Rodda, author of Deltora Quest. Eventually spawned a little series of five books: Rowan of Rin, Rowan and the Travelers, Rowan and the Keeper of the Crystal, Rowan and the Zebak, and Rowan of the Bukshah.

The plot of the first book:

Rowan is a small, weak, cowardly boy growing up in a village of big, strong, coward-despising men and women. Heck, even Rowan's little sister is braver than he is! So Rowan is given a job befitting someone half his age: taking care of the bukshah, the bison-like pack animals that provide the village with milk, cheese, wool, and strong backs to plow the fields and carry goods to market once a year.

Then, at the start of our story, the stream that comes down from the mountain stops flowing. The village has a well, so the people will be fine, but the bukshah can't drink well-water; they need the "sweet water" from the mountain stream. And without the bukshah, the village will have to move. Since this has been their home for many generations, they decide to send a few brave souls up the mountain to see if they can't figure out what is blocking the source of the water. This decision is a hard one, for the mountain is known to contain deadly threats, and no one who goes up there returns. Well... except for crazy Sheba, but she's, well, crazy.

Five big, strapping villagers volunteer, along with the less strapping but still quick-witted Allun (whose mother is from Rin, but whose father was a skinny Traveler). They're all set to head out in the morning, and decide to get some advice from Sheba, since the old shaman has managed to climb up the mountain repeatedly and is still here to talk about it. Sheba goes into an oracle's trance and relays a cryptic rhyme (the plot-governing rhyme is to become a hallmark of the series). She then contrives to give them a map... the contents of which disappear if held by anyone but young Rowan.

Soon it's decided that, despite the danger, Rowan must accompany the little group up the forbidden mountain. He's rightly terrified, but tries to concentrate on the reason for the mission: to bring fresh water back for his beloved bukshah.

The team heads up. And soon they find that the map spits out rhymes at them for every new danger they face. Sadly, its cryptic messages are often understood a little too late, and half the crew doesn't hold by stupid magic maps anyway. But let's see what they face:

A forest covered in giant webs, with spiders as big as your hand.
A swamp that tries to trick you off the path with visions of your loved ones dying.
A giant cliff, which seems to offer no way up at all.
A cave that delves deep into the mountain.
An underground lake, cold as ice.
A treacherous path that nearly leads them to their deaths.
A tiny, winding tunnel, so small they can't even crawl on hands and knees, so long it takes three days to pass.
And finally... the top of the mountain, and... the Dragon.

A key point of the plot, though, is that at each step, the party loses another member to one fear or another. Arachnophobia is the simple one; from there, we get fear of the supernatural, fear of being apart from her twin brother, fear of being laughed at (that one causes a crucial missing skill, because of the fear's effects a decade or more ago), claustrophobia... even Strong Jonn succumbs in the end, though his fear isn't so clearly stated as all that. And finally it is Rowan alone who's left to carry on the mission, to face the greatest fear and overcome it for the sake of those left below.

Tropes used in Rowan of Rin include:

Cowardly Lion: Rowan is afraid of everything. Which means he faces his fears every single day, which means he's the only one brave enough to make it all the way to the end.
Fearless Fool: In an excellent twist, John is beaten by the mountain not because he was afraid, but because he wasn't and should have been. Exhausted and slowly freezing he realizes that Sheba was right, only fools do not fear, and admits this to Rohan.
Hypocrite: Towards the end of the first novel, the characters are back home worrying about Strong Jonn; Val states that he's 'all alone' on the mountain. Allun points out that he's not alone, Rowan's with him. Val sneers that a weakling like Rowan is no use to Jonn, and he needs someone strong, brave and courageous by his side at a time like this. Allun bluntly points out that Jonn had five strong, brave and courageous companions at one point: "They all ran away." Val, who was among the first to run away, has no comeback to this.
Jerkass: Naturally,Kids Are Cruel towards Rowan, but plenty of the adults are also unnecessarily mean to Rowan as well.
Miles Gloriosus: Most of the villagers prize heroism and bravery, and look down on Rowan because he wears his fears on his sleeve, but some meet this trope more than others; in particular, Marlie, Allun and Jonn are more understanding of Rowan. Tellingly, although each of those who accompanies Rowan on the journey have their own well-hidden terrors to face, those who are cruelest and most dismissive of Rowan tend to have the most humiliating breakdowns and are those who are forced to drop out first.
The So-Called Coward: A variation; Rowan is genuinely terrified by his adventure, and is the subject of contempt from those around him because of his fear, but manages to pull himself together enough to make it through.
Take Off Your Clothes: Strong Jonn, Marlie, and Rowan just swam through an underground ice-cold lake, and on the other side Marlie is all businesslike about, "Let's change clothes immediately so we don't get sick." — but Rowan just utterly refuses. Marlie's astounded by this: the whole crux of the plot is about overcoming fear, and they've been through X number of horribly frightening things so far, and how can Rowan think this is a big deal? But Strong Jonn knowingly tells Marlie to turn her back so that modesty can be preserved.
Why Did It Have to Be Snakes?: Each of the main characters has their own 'snake' to face over the course of the journey.