Is there a single word describing someone who is like a frog in a well? The frog believes the well is the entire world. How can I describe people who think that their own small environment is the entire world?
Synonyms of parochial, “characterized by an unsophisticated focus on local concerns to the exclusion of wider contexts”, may serve. Such synonyms include confined, insular, limited, local, narrow, narrow-minded, petty, provincial, regional, small-minded, isolated.
Insular, for example, has a sense that means “separate or isolated from the surroundings; having little interaction with external parties; provincial.” Narrow-minded and small-minded are of course easily understood, and so would be close-minded.
Blinkered, fitted with blinkers, or “eye shields attached to a hood for horses, to prevent them from seeing backwards and partially sideways”, is another possibility, as are formations from synonyms blinders and winkers.
Edit: Also consider monomania, “excessive interest or concentration on a singular object or subject” or “a pathological obsession with one person, thing or idea”; obsession, “compulsive or irrational preoccupation; an unhealthy fixation”; idée fixe;
tunnel vision, “an extremely narrow point of view; narrow-mindedness”; and locked-in.