Dickens is reinforcing the need for imagination and fantasy in one’s life.
One of the key issues in Hard Times is of the importance of imagination and individuality. Dickens wrote the book as a protest to what industrialized society was doing to people. Sometimes the cold, hard, facts are not enough. Sometimes we need imagination and fantasy.
Sissy is described as “grown learned in childish lore; thinking no innocent and pretty fancy ever to be despised” (Book 3, Ch 9/ch 37).
Unlike the other characters, Sissy never gave up on imagination. She was the only character that had a happy life. She was happy because she embraced her imagination. Dickens is encouraging his readers to re-consider and industrial life of facts.
Dickens says that:
[People need] to beautify their lives of machinery and reality with those imaginative graces and delights, without which the heart of infancy will wither up, the sturdiest physical manhood will be morally stark death. (Book 3, Ch 9/ch 37)
In Victorian London, progress was the common refrain. Progress was efficiency, in schools, factories, and lives. Efficiency, Dickens argues, can never supplant humanity. The results are disastrous.