Quote 19
I kneel beside Boggs, prepared to repeat the role I played with Rue, with the morphling from 6, giving him someone to hold on to as he's released from life. But Boggs has both hands working the Holo. He's typing in a command […] A green shaft of light bursts out of the Holo and illuminates his face. (20.6)
Boggs has just had both legs destroyed in a bomb. He's dying, and in a terrible way. Yet he still clings to life to accomplish one final task as a soldier and serve his cause by giving control of the Holo to Katniss. If he doesn't do so, it will be unusable. The fact that Boggs can put aside the incredible pain and terror of dying to focus on his duty shows just how courageous he is.
Quote 20
Having no work, grief buries me. All that keeps me going is Coin's promise. That I can kill Snow. And when that's done, nothing will be left. (25.15)
Katniss can only carry on because of one thing: the idea that she "can kill Snow." She can stay present and focused because of that goal, but that's it. Her courage will only take her that far. Once she's accomplished that last mission, she'll collapse back into her "grief."
Quote 21
My finger catches the inside of my bracelet, twisting it like a tourniquet, hurting my wrist. I'm hoping the pain will help me hang on to reality the way it did for Peeta. I must hang on. I must know the truth about what has happened. (26.2)
From Peeta, Katniss has learned a new way of being brave. It's brave to confront "reality." It's brave to want to "know the truth." The pain Katniss feels in her body mimics the pain she feels inside when she's trying to confront such ideas. It would be easier to disassociate from reality and not try to figure out the truth. But to do so, though, would not honor Prim.