Hazel Grace meets Augustus Waters in the first chapter of Green's The Fault in Our Stars. The first step to their expected romance can be found in Hazel's attraction to Augustus, which is expressed as follows:
"Look, let me just say it: He was hot. A nonhot boy stares at you relentlessly and it is, at best, awkward and, at worst, a form of assault. But a hot boy . . . well" (9).
The next thing that needs to happen in order for the expected love affair to start is for Augustus to declare his attraction to Hazel, which he does as follows:
"'Why are you looking at me like that?' Augustus half smiled. 'Because you're beautiful. I enjoy looking at beautiful people, and I decided a while ago not to deny myself the simpler pleasures of existences'" (16).
Augustus declares that he won't deny himself of simple pleasures, which also suggests that he won't allow anything he wants in life to get away. This subtle hint foreshadows that he won't let Hazel get away; therefore, the romance can be predicted and expected from this point going forward.
As stated in the previous answer, the death of Augustus is unexpected based on the fact that Hazel's condition seems to be worse than his throughout the novel. Another unexpected twist to be discussed, then, is the way Hazel and Augustus are treated when they meet her favorite author Peter Van Houten in Amsterdam.
From emails apparently sent by Van Houten, the kids believe they are cordially invited to meet the author of An Imperial Affliction. Unfortunately, they discover that the one being cordial to them is not Van Houten but Lidweij, his assistant. Even though Van Houten does not invite Hazel and Augustus to meet him, it is completely unexpected for him to treat the kids with such angst and disrespect--especially when he says the following:
"Sick children inevitably becomes arrested: You are fated to live out your days as the child you were when diagnosed, the child who believes there is life after a novel ends. And we, as adults, we pity this, so we pay for your treatments, for your oxygen machines. We give you food and water through you are unlikely to live long enough . . . You are a failed experiment in mutation" (192-193).
No one expects an adult to speak to dying children like this. Even though Van Houten is a sorry excuse for a man, he crosses a line by saying what is in the above passage.
Furthermore, it is unexpected to see Hazel stand up for herself with such gusto when she holds Van Houten to task as follows:
"Listen douchepants . . . you're not going to tell me anything about disease I don't already know. I need one and only one thing from you before I walk out of your life forever: WHAT HAPPENS TO ANNA'S MOTHER?" (193).
The situation escalates quickly, and Augustus ends it by taking Hazel out of the house immediately. This scene between Van Houten and Hazel is certainly unexpected; however, the strength of the expected love and bond between the young lovers supports Hazel through this disappointing meeting.