Saju (the "four pillars") means literally four pillars: it is a traditional Eastern study that reads one's innate temperament and the flow of fortune over a lifetime, taking the year, month, day, and hour of birth as four pillars. Each pillar pairs one Heavenly Stem (the energy of heaven) with one Earthly Branch (the energy of earth), yielding eight characters in all—hence the common name "saju palja," the four pillars and eight characters. These eight characters are like a single photograph capturing the cosmic energy of the very moment a person came into the world.
The philosophical roots of saju reach into yin-yang and the five elements and into the refined calendrics of ancient East Asia. At first fortunes were read centering on the year of birth; Li Xuzhong of the Tang dynasty refined that framework, and by the Song dynasty Xu Ziping established today's system, taking the Heavenly Stem of the birth day—the day master—as the person themselves and interpreting it through its relations with the other characters. For this reason traditional saju is also called "Ziping" astrology, after his name.
This study passed from China to Korea and Japan, taking deep root in each culture. In Korea especially, a custom of consulting saju at the important crossroads of life settled in over long ages. When a child was born, a missing energy would be supplied in choosing a name; before a marriage, the two people's charts would be compared for compatibility; and for great affairs such as moving house or opening a business, an auspicious day would be chosen. Saju was regarded not as mere fortune-telling but as a wisdom that reads both a person's temperament and the flow of time to live life well.
The common way to misunderstand saju is to receive it as a "fixed script of the future." Yet even traditionally, saju was understood not as a tool that nails down fate but as a map of one's innate temperament and a weather forecast of time. Just as, hearing the same forecast of rain, the day of one who brings an umbrella differs from one who does not, the result changes greatly depending on how you meet the flow saju reveals and what you prepare. Filling a lacking energy through your attitude and surroundings, and not missing a good time—that is the original purpose of studying saju.
As for its present, saju is loved as steadily as ever. Thanks to apps and online services that instantly handle the complex calendar calculations, anyone can easily check their own eight characters, and at the crossroads of life—career, a job change, marriage—it remains a reliable reference for those seeking to understand themselves more deeply. As with Western astrology, saju stays beside us not as a yoke that confines but as a warm mirror that reflects us and helps us choose better.