Duncan came under the service of the Atreides after observing that they ruled in stark contrast to the Harkonnens. The Atreides appeared to garner fierce loyalty from those who served them, and Duncan was no different. However, as Atreides Swordmaster he maintained a hypervigilance against potential threats to the Atreides, even within their own ranks. As a result, he developed a distrust of the Lady Jessica, as he knew that her Bene Gesserit origins were likely to involve some secret scheme against the Atreides. However, Duncan underestimated Jessica's love for her Duke, which was so strong that she disobeyed her Sisterhood. Indeed, in matters regarding the Lady Jessica, Duncan's judgment was somewhat clouded, since he was secretly in love with her.