Hardy's novel pits the forbidding Egdon Heath against the people who live there. The heath, in its barrenness and indifference to humanity, is evidence of how humans are simply another aspect of the natural world, and that identity and desire are subordinate to the environment. In this sense, the heath is a kind of tabula rasa—a blank surface on which characters project what they want to see. It becomes clear that the escape Eustacia yearns for is illusory—her antipathy to the heath is a kind of projection of her own unfulfilled desires, and there is little reason to suppose that an escape from the heath would make any difference. What she seeks to escape is not the heath, but herself.

Hardy's "pessimism" can be linked to the ineffectual yearnings of these characters. While Clym and Eustacia, in their different ways, each yearn for fulfillment, this desire is irrelevant. Much of the tension of the novel comes from the passion with which the characters struggle against their situation, and how these struggles simply do not matter in the larger scheme of things. I'm not sure that "pessimism" is the right word for this, however. Pessimism suggests that one has doubts, but in Hardy's universe there are no doubts: the world, in the form of the heath, will always grind down the people who live there. The only way out is to opt out—as Eustacia does when she kills herself.