I've seen most of these books mentioned in this thread, but I'm going to explain more on 'why' they might be considered life changing.
7 Habits of Highly Effective People - Stephen CoveyI experienced a paradigm shift after reading the first chapter alone. I read this when I was stuck in a pretty bad rut of depression & depersonalization. This book helped me understand that my mental turmoil and circumstances were the result of my choice in the matter.
"We must look at the lens through which we see the world, as well as the world we see, and that the lens itself shapes how we interpret the world."Man's Search for Meaning - Viktor FranklFrankl presents material that could only be achieved when people are pitted into the darkest hours of human existence. This is not your typical modern self-help book. This is a deep exploration into the psychology of purpose and meaning. As a bonus, the book provides tons of references on the subject for further reading. Frankl is a renowned psychologist, and this text is significant in the field of psychology.
The Alchemist - Paul CoelhoIt's a fantastic fiction book. I listened to it on Audible. It delves into the idea of a 'personal legend' which I thought was applicable when thinking about my own life. I came away from it feeling inspired to forge direction in life.
Book of Five Rings - Miyamoto Musashi (translations by Alexander Bennett)This is a book about strategy that was written sometime in the 1600s. The book itself is about the strategy of swordsmanship, but can easily be applied to learning something new, honing a skill, building a business, playing a sport competitively, etc. Tons of value and wisdom in this book.
One book that I'm a bit surprised hasn't been mentioned, so I'll mention it:
12 Rules for Life: An Antidote to Chaos - Jordan B. PetersonI'm putting up a
major asterisk* when suggesting this one. JBP has become somewhat of a controversial public and political figure. Seems to me he got tangled up in the media, then the pressure of fame got into his head and caused him to regress as a person. I recommend reading this book at its surface without digging into the author's political and public influence. It's a book about the relationship between responsibility and meaning. If getting serious about putting your life together and becoming the best version of yourself are ideas that resonate with you, you will enjoy this book.