This is such a good question! The first one that comes to mind is The Humans by Matt Haig. It's a very underrated book in which an alien has to disguise themselves as a human, and in the process of doing that he learns what being human really means. I read it for the first time in my teens, and it really changed me a lot. I believe it is one of the first books that helped me start my journey into looking at humanity in a more positive light and to appreciate the small things in life. Thinking about it it was the first book that helped start a process of shifting my perspective in focusing on the small joys. That cycle continued with my love for hobbits which have become the model of how I want to enjoy life. The small comforts and pleasures that we often tend to take for granted. The books that mark the end of this cycle and my arrival at fully living with this mindset are the two Monk And Robot books by Becky Chambers (A Psalm For The Wild Built and A Prayer For The Crown Shy). This duology is so healing for me. I love every single thing about it, and they act as a reminder for many many important things. Like the fact that existing to enjoy a good cup of tea is enough purpose for a life worth living. Once again it celebrates the pure joy of small things and reminds me that being a small creature on this big big planet is not bad at all. I am surely forgetting about some important books that influenced me in some way, but I feel like these outline a very specific set of feelings that I managed to embrace thanks to books only. They really shaped the person I am and they are reminders for me. So much so that I have many quotes written in my commonplace book, where I reread passages when I need some comfort.