Great question! This statement identifies the way that the circus people and Bounderby and Gradgrind are set in opposition against each other, one championing the power of the imagination and make-believe, the other championing the power of utilitarianism and the dominating force of "Facts." A chapter you will want to examine very carefully is Chapter 6 in Book the First, entitled "Sleary's Horsemanship." One aspect that is noteworthy about this chapter is the symbol of the Pegasus, the flying horse of Greek legend, that gives its name to the public house frequented by the circus folk. Note the description we are given of the pegasus on the wall in the public house:
Framed and glazed upon the wall behind the dingy little bar, was another Pegasus - a theatrical one - with real gauze let in for his wings, golden stars stuck all over him, and his ethereal harness made of red silk.
Key to remember is that in Chapter 2 we were given a very precise, utilitarian definition of a "horse." Let us also remember that in this same chapter Gradgrind tells his students authoritatively that any wallpaper with horses on it is unrealistic because horses do not live on walls. In contrast to this reductionist view of the world, the Pegasus symbolises the kind of world that the circus people live in - a world of fantasy, of make-believe, a world where horses dance the polka and can fly. Crucially, this is a world from which the Gradgrind children are excluded. Thus the very name of the public house reinforces this division between fact and fantasy, between imagination and drudgery and between joy and coldness. Note how Sissy is shown to have experienced real human warmth and love from her circus family - love and warmth that have never been experienced by Tom and Louisa.