In Chapter 1, Carroll demonstrates the vast difference between Alice and her sister. Her sister sits quietly on the riverbank, absorbed in her book, while Alice grows impatient with reading. She picks flowers and tries to amuse herself with her imagination. Just as she begins falling into a reverie, she spies the old White Rabbit:
So she was considering in her own mind (as well as she could, for the hot day made her feel very sleepy and stupid), whether the pleasure of making a daisy-chain would be worth the trouble of getting up and picking the daisies, when suddenly a White Rabbit with pink eyes ran close by her.
Here, Carroll hints at the fact that Alice is falling asleep. But he does not explicitly mention that her "sleepy and stupid" state leads to sleep, so readers do not officially find out that Wonderland was a dream until the final pages. The dreaming Alice believes that she has actually fallen down a rabbit hole and must figure out how to navigate a crazy new world in which nothing meets her expectations.
From the first scene, readers might assume that this would never happen to her sister, who remains firmly rooted in reality. The difference between Alice and her sister suggests that creativity wanes with age. The foil between these characters also shows which kind of person is more likely to have exciting and fulfilling (if sometimes dangerous) life experiences. It signifies the gradual loss of imagination as one grows older.