It is true that at first Templeton the rat refuses to help Wilbur. Templeton has been characterized in the book from the start as a creature who only cares about his own well-being. For example, when Wilbur asks him to play, Templeton responds,

"Play? I hardly know the meaning of the word."

"Well," said Wilbur, "it means to have fun, to frolic, to run and skip and make merry."

"I never do those things if I can avoid them," replied the rat, sourly. "I prefer to spend my time eating, gnawing, spying, and hiding."

He calls himself a glutton rather than a merrymaker. Food is primary interest in life.

The other animals know that Templeton cannot be trusted. As they understand,

The rat had no morals, no conscience, no scruples, no consideration, no decency, no milk of rodent kindness, no compunctions, no higher feeling, no friendliness, no anything.

This selfishness and hardness come into play when the other animals need the rat's help in saving Wilbur. The oldest sheep knows Templeton visits the dump regularly and could bring back scraps of old magazine ads with words that Charlotte could then weave into her web. Charlotte, however, is doubtful the rat will want to help, saying he only looks out for himself, never anyone else.

True to form, Templeton scorns the idea of exerting himself to save Wilbur, saying "let him die." But the wise old sheep understands how the rat's mind operates. She tells him that it is in his own self interest to help save Wilbur's life. She reminds him that Wilbur's food is the rat's food—he eats the leftovers of Wilbur's warm slops, which will be missing if the pig is killed. This raw appeal to Templeton's own needs convinces him to help. Later, stories of the fair as a rat's heaven of leftover food will convince him to go there.