Hunger by Knut Hamsun, 1890. I consider it the first psychological novel.
"The novel has been hailed as the literary opening of the 20th century[1] and an outstanding example of modern, psychology-driven literature.[2] Hunger portrays the irrationality of the human mind in an intriguing and sometimes humorous manner."
https://en.wikipedia.org/wiki/Hunger_(Hamsun_novel)
"The novel has been hailed as the literary opening of the 20th century[1] and an outstanding example of modern, psychology-driven literature.[2] Hunger portrays the irrationality of the human mind in an intriguing and sometimes humorous manner." https://en.wikipedia.org/wiki/Hunger_(Hamsun_novel)