What oppressive force is at work in Anarresti society that influences how individuals act in The Dispossessed by Ursula K. Le Guin? How does this force relate to Freud’s tripartite model? How specifically does this force influence individuals?

According to Freud's tripartite model, the psyche consists of three parts: the id, ego, and superego. The id operates under the pleasure principle; regardless of the consequences, the id wants to satisfy every desire immediately. On the other hand, the ego operates under the reality principle; it is primarily concerned with pragmatic considerations in satisfying the id's demands. It should be noted that the ego considers societal norms and etiquette in its deliberations. The superego consists of the ideal self and the conscience, which are both determined through upbringing and parental influence.
In Le Guin's book, Odonian idealism has to exist with an equally opposing force: gratuitous self-interest. As a character, Sabul exemplifies what happens to individuals who are influenced by it.
Accordingly, Shevek learns Sabul is actuated by a personal desire for aggrandizement; the older man orders Shevek to hide his newly-acquired knowledge of Urrasti physics and Iotic from other scientists. The truth is that, without fluency in Iotic, no Anarresti scientist can delve into the concepts of Urrasti physics. For his part, Sabul wants to preserve this status quo of affairs. In desiring to use his knowledge of Urrasti physics as a source of power over his colleagues, Sabul is operating under the pleasure principle. With Sabul, the id's demands take precedence over the ego and superego's demands. By appropriating other scientists' work for his own, Sabul rejects the traditional Anarresti concepts of mutual reliance, solidarity, and disinterested benevolence.
Sabul is definitely an example of how this oppressive force influences individuals adversely.