The Bell Jar is a metaphor showing that Esther (the main character) is trapped inside her own head and cannot escape her insecure thoughts.
The Bell Jar was Plath’s debut novel, written in 1963. The book is a psychological autobiographical novel that reflects her mental health  struggles. The Bell Jar is a metaphor showing that Esther (the main character) is trapped inside her own head and cannot escape her insecure thoughts.