As the Games begin, Finnick quickly proves that Katniss can count on him as an ally, suggesting Haymitch may have brokered some sort of deal behind her back. Right from the start, when Katniss and Finnick first come face to face, Finnick already has it in mind that they should work together. He suggests as much when he says it’s a good thing they’re allies, and then he actually proves it when he kills a tribute who is coming up on Katniss from behind. He also shows that he’s willing to protect Peeta. He swims out to retrieve Peeta when Peeta is stuck on the metal platform in the middle of the water, and more notably, he revives Peeta after his heart stops from the shock of the force field. It’s possible, of course, that Finnick recognizes how strong an ally Katniss could be and that she would only partner with him if he looked out for Peeta, but the bangle Finnick wears suggests that Haymitch is somehow involved in his looking out for Peeta and Katniss. It’s the same bangle Effie gave Haymitch so they would all look like part of a team, and Katniss knows Haymitch’s method of communicating well enough to know that he’s signaling to her to trust Finnick.
In fact, the sacrifices other tributes make for her and Peeta are bewildering to Katniss, and they imply that something’s going on which Katniss doesn’t know about. As Katniss recognizes after Finnick resuscitates Peeta, Finnick had no good reason, at least that she knows of, to revive Peeta. Peeta’s death, had it occurred, wouldn’t have been Finnick’s fault, so he didn’t need to worry about Katniss using it as an excuse to break their alliance. He also essentially saved an enemy whom he would later have to kill or who might kill him. Mags also sacrifices herself for their benefits. She may have known she wouldn’t survive the Games because of her age and frailty, but if her concern was just for Finnick, the two of them could have easily survived by running away and leaving Katniss and Peeta to die. Instead, she removed herself as a burden, allowing Finnick to carry Peeta out and letting Katniss only have to bring herself to safety. Lastly, the female morphling addict from District 6 clearly sacrifices herself to save Peeta specifically, but why she would do it is uncertain. All of these events suggest an effort by at least some of the tributes to help Peeta, or Katniss and Peeta, survive.
Katniss focuses primarily on keeping Peeta alive as the Games get underway, and she realizes quickly that she can’t do it on her own. Right from the start Katniss sees that Peeta may be at a disadvantage in the arena. For instance, because he seems not to know how to swim, or because he’s now unable to swim since losing his leg in the first Games, he’s stuck out in the water. Despite the risk to herself, Katniss doesn’t hesitate to go get him, but it’s actually Finnick, a much stronger swimmer than Katniss, who dives in and fetches him. Later, after Peeta gets shocked by the force field and his heart stops, Katniss doesn’t know how to help him. But Finnick revives him, causing Katniss to recognize that, without Finnick, Peeta would have died. This last event forces Katniss to acknowledge that she might not be able to keep Peeta alive by herself, and that realization leads her to temporarily break down in tears as she comes to terms with how limited her control is. That point is underscored twice more in the section. As Katniss and the others run from the fog, it’s again Finnick who essentially saves Peeta, and their survival is only possible because Mags sacrifices herself. Finally, during the monkey attack, the woman from District 6 also sacrifices herself, jumping in to intercept the monkey that would have killed Peeta. The lesson to Katniss is that, if she does intend to keep Peeta alive, she has no choice but to accept help from others, which also means trusting them no matter how uncomfortable it makes her.
The willingness to kill each other that many of the other tributes show at the Cornucopia is a great disappointment for Katniss, perhaps because of what it represents as much as the actual violence. Finnick reminds her that none of the tributes won their Games by chance, implying that they’re all to some degree born killers. But Katniss’s disappointment appears to go deeper than just objecting to their readiness to attack one another. Their display of unity in the interview with Caesar Flickerman was a kind of revolt against the Capitol, and Katniss thought it might also provide some encouragement to the rebels. That the tributes have all cast aside that unity and are fighting each other dispels that sense of solidarity. Moreover, they’re doing exactly what the Capitol wants, which again emphasizes how much power the Capitol has over the people of Panem, even the ones who are willing to stand up to it.