I recommend "Staring At The Sun: Being at peace with your own mortality", by Irvin Yalom. The book encourages readers to confront their fear of death rather than avoid it. It helped me in my personal development, in the sense that it gave me a new perspective on my depressive and fearful side and a new outlook on life. It has substance, it's not a typical airport kiosk read. Yalom's thoughts are deeply rooted in existential philosophy and blend psychological concepts with profound philosophical reflections.

Witold Gombrowicz, Diaries (it's a diary of a Polish writer in exile, but there is a lot of self-development inspiration you can find in it)

"How to Win Friends & Influence" people was the difference between me staying in the dorm alone and making friends while I was in uni dorms for 1 semester (and I wasn't going to courses either)

I had some social anxiety and "How to Win Friends & Influence" people was the difference between being a loner in my dorm and making friends while I was in uni (I didn't go courses either, but I was able to live in a dorm for 1 semester)