In the first episode, it's revealed that Forte's character, Phil, has been traveling the United States looking for another living human that has survived an (almost) extinction level cataclysm. After two years, he returns to Tucson, AZ and tries to find a way to live a life alone on the planet. Despite having access to a seemingly endless supply of preserved food and drink, by the end of the pilot episode, he is on the verge of suicide.
This is the apotheosis of Emile Durkheim's observation in his seminal sociological study of suicide. In this work, Durkheim argues how the intensively private act of suicide is actually fundamentally shaped by social forces. Durkheim notes,
To free him from all social pressure is to abandon him to himself and demoralize him...(into) a general state of extreme depression and exaggerated sadness, causing the patient no longer to realize sanely the bonds which connect him with people and things about him. Pleasures no longer attractIn this case, it's not a false perception of social isolation, But the actual loss of all possibility of social contact pushes Phil to end his life.
Further, it seems that one of the most troubling symptoms of the loss of sociality is the loss of symbols, or meaning. In a quote I really, really like, Clifford Geertz notes that humans
without the assistance of cultural patterns (i.e. symbols-my addition) (w)e would be functionally incomplete, not merely a talented ape who had, like some underprivileged child, unfortunately been prevented from realizing his full potentialities, but a kind of formless monster with neither sense of direction nor power of self-control, a chaos of spasmodic impulses and vague emotions [1973:99]*In the show, there are a few nice little touches about the loss of meaning in a world newly devoid of people. In his cross-country trek, Phil collected an RV load of artistic and historical items...items whose meaning becomes meaningless once almost all people are gone. The contrast between Phil and Kristen Schaal's character, Carol, riffs on this insight. Carol still holds to much of the systems of meaning of the past world, from the banal--appropriate parking etiquette--to the more obvious--marriage. Phil represents the formless monster who fills his day with pornography, beer drinking and defecation into a swimming pool. This monstrous condition allows him to understand the ridiculousness of continuing to consider the world's symbols meaningful as the social world that imbued with meaning is now gone. However, Carol and her continued action shaped by meaning seems all the more human because of it.