Why does tuck only smile in his sleep in tuck everlasting?

In "Tuck Everlasting," Tuck only smiles in his sleep because he is at peace and free from the burdens of immortality. When awake, he grApples with the consequences of living forever, including the loss and sorrow it brings. His smile in sleep symbolizes a fleeting moment of happiness and a return to innocence, away from the struggles of his eternal existence. This contrast highlights the emotional toll of immortality on him and his family.