I'll start. Sapiens by Yuval Noah Hariri - a book about big history, in light of the evolution of man and society.
This book introduced me to the concept of human nature and showed me that humans all over the world are fundamentally the same despite the cultural diversity of the world. People follow certain "fictional realities" like institutions, money, etc, concepts of which exist solely in our collective minds, and yet feel as real as nature.
Following this book, I picked up others that went into more detail about human nature, and that has greatly improved my emotional intelligence and people skills.