In Eye of the Needle, David Rose illustrates the hazards of social isolation in his interactions with Henry Faber. David is sent falling to his death with the words "It's not fair!" on his lips and the words "there's a war going on" ringing in his ears. David retired to the isolation of Storm Island as an honorable British gentleman expecting that all men he would encounter were also honorable gentleman. This blind generosity and trust allowed Faber to penetrate David's isolation and twist it to own purposes in fulfilling his mission resulting in David's death under protest.
Lucy Rose went with her husband David into social isolation on Storm Island and, in Faber's words, lost her ability to dissemble in the few short years of her sojourn there. Dissemble means to conceal truth or give misleading impressions. In an ironic twist, it is Lucy's inability to distrust that ultimately saves her from Faber and leads to Faber's own undoing.
Henry Faber has imposed isolation upon himself in a single-minded dedication to his mission. He has starved himself of human social contact. As a result, Lucy unnerves him and he cannot bring himself to kill her. This inability to continue his isolation ironically leads to ultimate failure in his mission.