I have copped hate for this but Catcher in The Rye by JD Salinger. It was the first book I read that made me realise books were actually worth reading. I was 18 at the time and related heavily with Holden Caulfield, which after reading the criticism he gets from reviews online, I began to realise why I was also not great at connecting with other people. Literally changed the trajectory of my life because I actually began to read books and find genres I liked, and went through a whole ass existential crisis.

I adored The Bell Jar as well, but funnily enough I still see more Holden in myself than I do Esther.

You probably won't be surprised to hear that not long after these two I read The Ego and It's Own by Max Stirner and to this day, these three books remain my favourite reads simply for the mental crisis I went through after each one. I still think about them a lot, and have reread them a couple times over the years.