In Chapter Twelve of Tuck Everlasting, Tuck takes Winnie out onto the pond in a rowboat just as the sun is setting. They bear witness to the different kinds of wildlife and the natural world around them, and Tuck begins to tell Winnie that life is a wheel which has its natural cycles of beginnings and endings; this is organic and the way that the world is intended to be.
The boat slides into a tree and stops moving, at which point Tuck compares his family to the boat. They have defied that natural order of things by becoming immortal. He is unhappy with this fact and believes that it is a violation of the way life is intended to be. He does not want to live forever.
Winnie, on the other hand, is frightened of the idea of death and wishes that she could become immortal, too. Tuck attempts to explain that the fact that his family will not die is "wrong." Ultimately, he wants Winnie to weigh her decision very carefully before she commits to drinking the water and seizing immortality for herself.