Never again could Zusak write with that in mind but with success comes fans and with fans comes expectations. Hopes were high for whatever Zusak produced next but with a worldwide audience waiting for his next masterpiece, how could he possibly meet their expectations?
Of course, the anticipation may not have been so high had it not taken Zusak 13 years to write his follow-up. Bridge of Clay was easily one of the most-anticipated novels of 2018.
Coming in just over 600 pages, with a cast of characters that spans continents and time periods, it's perhaps unsurprising it took Zusak so long to complete. It was a book he started in his early 20s, before he even conceived the idea for The Book Thief, but the central ideas in it proved so fiddly that he kept putting it aside.
"I just had this image of a boy wanting to build a bridge and wanting to make it perfect. When you've got a character striving for perfection in a story, you feel you have to achieve that in the writing as well," Zusak says.
That boy is the titular hero Clay but his journey stretches well beyond the bounds of this teenaged boy in suburban Sydney. Clay is one of five brothers; his mother has died, his father has vanished, and their presence in the Dunbar house has been replaced by a menagerie of animals including a moulting cat and a stubborn donkey.
The story moves between multiple timelines and various perspectives, telling not just Clay's story and those of his brothers, but going back through their parents past as well. With so many characters, the struggle to perfect the story and do justice to each individual weighed on Zusak.
"I had a crack at writing the book in my early 20s, and I finished it, but I think you spend so much of your life as a writer searching and writing and going, 'That's not it, that's not the book.' And then you try again and that's not it either and then you try again."
The idea was put aside but after The Book Thief, Zusak struggled to think of any other ideas and Clay and his bridge was all that he had left – now, with the added fan base and critical and commercial expectations that came with a bestseller.
While The Book Thief had the challenge of seeming unreadable, Bridge of Clay had the opposite challenge - Zusak knew people were going to read this one - and it presented him with a conundrum: did he write a book to please those people or write it as it must be written? He says he eventually had to cross a line and accept he couldn't please everyone.
Bridge of Clay is a story of family and friendship, one of hope and expectations, one that unpicks the very nature of stories and being, how the past has power over the present.
"I found myself really drawn to these stories, telling our origins further back then where we are now," Zusak says, reminiscing about how his parents (both European migrants to Australia) used to tell him stories around the dinner table.
It's a habit Zusak passed on to Clay and Penelope, the Dunbars' mother. She is a frequent storyteller, with her life in Austria during the Cold War and eventual escape a powerful influence on her son.
While Zusak and Clay are both the fourth-born in their families, that and the stories is where Zusak draws a line between the two. He says Clay is much "tougher" with a rougher childhood and excels where Zusak naturally struggles.
"Whatever bits and pieces of myself that I put into him, they're just spare parts of me that make him function. He's a character within himself."
Zusak definitely makes Clay suffer, often at the hands of his three older brothers and others from the neighbourhood. A memorable scene early in the story sees local boys take bets on whether Clay can run a lap around the local track, with other boys positioned to try and stop him as roughly as possible.
The brutal imagery feels pertinent to the current climate, touching on elements of toxic masculinity. Yet that's just another side-effect of how long it took to write the book; Zusak says exploring that particular theme was never his intention.
"Five brothers together - there's going to be some toughness. There are a lot of tender moments between the brothers as well," he says. "In hindsight, I wanted to write boys not only how they are but how we want them to be."
While a lot has changed during the past 13 years, the need to promote his books has not. Zusak is back on the festival circuit, which includes a visit to New Zealand with stops in Christchurch, Dunedin and the Auckland Writers Festival.
"As a writer, you spend so much time on your own. It's more of a joy meeting people at these festivals. You're getting out into the world again and that's where you start to fill up the well again for new writing."
Meeting people, talking about the book - that all means having to address those expectations. Bridge of Clay has similar elements to The Book Thief but the grander scope, coupled with a more lyrical prose, equates to a much different beast.
"I think I reached a turning point halfway when I thought 'I'm writing this book for Clay now, I'm writing it for Penelope, I'm writing for that whole family'," he says. "I know it sounds preposterous, as these are people who don't exist, but this is why I became a writer in the first place. That moment when you're reading a book and you know it's not true, but you believe it when you're in it."
While the fans are important, for Zusak, what counts most is that he did justice to Clay, Penelope and the other Dunbar boys.
"By the end, I was writing it for them, and if you think that, then whatever happens out in the world will take care of itself, and whatever will be will be."
•Marcus Zusak appears at the Dunedin Writers & Readers Festival (May 9-12) and at WORD Christchurch (May 8-25) before travelling to the Auckland Writers Festival (May 13-21)
