Tuck has it kind of rough. He's been around a while (over a hundred years) and he's kind of getting sick of life. But because he's his family's leader and center, he has to stay strong.
Just like Winnie, Tuck has a dream, too. He dreams that things could be different. In fact, when we first meet him, that's exactly what he's doing—dreaming:
Tuck twitched and the smile vanished. He opened his eyes. "Why'd you have to wake me up?" he sighed. "I was having that dream again, the good one where we're all in heaven and never heard of Treegap." (2.4)
So this guy wants to die? This can't be good. Soon enough, we learn that he is immortal, and he isn't too happy about it. Although Mae urges him to accept his fate and move on—they can't change their immortality, so why fuss about it?—Tuck can't let it go. He can't stop thinking about what's happened to his family and what eternal life has done to them.
We're no certified practitioner, but we'd say he's bordering on depressed:
He was still asleep, and the melancholy creases that folded his daytime face were smoothed and slack. He snored gently, and for a moment the corners of his mouth turned upward in a smile. Tuck almost never smiled except in sleep. (2.2)
Life isn't really worth smiling about for Tuck. But when he meets Winnie, he smiles almost immediately. What's up with that? We're pretty sure that any connection to a mortal makes him happy—it makes him remember the happiness he once had, and that he wishes he could get back.
So why the beef with eternal life? As far as Tuck's concerned, immortality has made the Tucks' everyday life carry less value, less meaning. They still are alive, sure, but Tuck says that they're not "living." He tells Winnie:
"Living's heavy work, but off to one side, the way we are, it's useless, too. It don't make sense. If I knowed how to climb back on the wheel, I'd do it in a minute. You can't have living without dying. So you can't call it living, what we got. We just are, we just be, like rocks beside the road." (12.10)
According to Tuck, life just means more when you know it will end. You know how they say it takes sadness to really appreciate happiness? Well, the same thing applies here. Tuck would say that it takes the knowledge of your mortality to really be able to appreciate life.
What do you think, does Tuck need an attitude adjustment? Would he be happier if he just accepted his fate?
More than anyone else in the family, Tuck longs for the one thing they can't have: death. He even shoots himself right in the heart to see if it's possible. That's definitely a guy who isn't afraid of dying.
When Mae attacks the Yellow Suit Guy, Tuck isn't really fazed. Instead, he's totally fixated on the possibility of dying. Winnie watches Tuck as Tuck watches the dying man:
Tuck […] was gazing at the body on the ground, leaning forward slightly, his brows drawn down, his mouth a little open. It was as if he were entranced and—yes, envious—like a starving man looking through a window at a banquet. Winnie could not bear to see him like that. (20.12)
Tuck is envious of a dying man. For him, death is a longed-for, rightful end. And no matter what, he can't have it.
Tuck has the most time to chat with Winnie about being immortal, and based on her final decision, it sounds like she listened to him. But if Tuck is so convinced that mortality (and death) is the best route, why does he cry when he sees her grave? Sure, those might be tears of sadness for losing a member of his family, but we're pretty sure there's more to it than that.
That "lump in his throat" he has at her grave might just be due to some other emotions: happiness and relief. After all, before leaving the cemetery, he says, "'Good girl'" (Epilogue.23). Tuck is definitely happy that Winnie made the choice that he didn't have the option to choose. She got to do the things he wanted to do, and she made the choice he would've made. And guess what? He helped make that happen for her.