Your birth time is split into four units — Year, Month, Day, Hour. Each unit is a "pillar" made of a Heavenly Stem (top) and an Earthly Branch (bottom). That gives eight characters — BaZi literally means "eight characters."
The pillars represent different life domains:
- Year Pillar — your ancestry, heritage, outer social world, and early childhood.
- Month Pillar — your career, parents, and the environment that shaped you.
- Day Pillar — you (the Day Master) and your intimate relationships.
- Hour Pillar — your inner world, secret thoughts, children, and legacy.
Imagine a house: the Year is the roof, the Month the walls, the Day the living room where you dwell, and the Hour the hidden basement.