The first lesson that Hakkai learns from Gojyo is that there is a lot of room in a person's heart.
Hakkai knows that, on their journey, having such a big heart makes you vulnerable and, if this is so, then it means that Gojyo is the weakest of the four.
Hakkai sees the way that Gojyo's knuckles go white while he's clutching the dead boy in his arms, and some part of him registers that this must have been the way the Gojyo had carried him -- bleeding and limp, carrying him as if he were cradling glass -- and by the time they lay the boy in the ground and Goku picks up a shovel, Gojyo is lighting up a cigarette.
"There's no god," Gojyo says later, after the face of the dead boy is buried six feet under earth, leaning back so far in his chair that his head touches the wall, "just man."
In the dark of the room, all that Hakkai can see out of his good eye is the burning cherry of Gojyo's cigarette as it bobs in the dark. His own chair, rickety and worn, screeches when he pushes back and gets up, stretching. Up close, Gojyo smells like ashes and dirt and sweat; no one's had the energy to take a bath yet.
"Does this make me crazy, teacher?" Gojyo asks between drags, running a hand through his hair. "Or just a fool?"
"No," Hakkai finds himself replying softly, "it just makes you human."
Gojyo's mouth quirks upward, "And Kami-sama?"
Hakkai finds that Gojyo's shoulder is solid to the touch, and tense. "Sometimes humans are not that humane."
Gojyo buries his nose in Hakkai's side, and Hakkai can't help but shudder when Gojyo's hand feels for the scar through cloth and bandages.
Gojyo gives everything up so easily, he thinks as Gojyo's hand drops to fumble with the buttons. Hakkai can't give Gojyo real answers or enough love to make Gojyo's hands stop shaking; a youkai's heart is small -- so much smaller than a human's heart that Hakkai doesn't think that he has the room to hold as many people as close to himself as Gojyo does. All he can give, he tells Gojyo silently as he drops to his knees, is this.
The second lesson Hakkai learns from Gojyo is that, the second time around, it still hurts.