In the study of fate, the major luck period refers to the general fortune for each ten years calculated based on one's birth time and date.
Fate theory suggests that a person's fortune changes in stages, with a major luck period lasting ten years and a minor luck period lasting five years. A person's life goes through one major luck period after another.

When predicting the eight characters, we usually say that you start going through the major luck period at a certain age. Every time your age ends with a specific number, your major luck period will change and you will move into another major luck period.
For example, some people start going through the major luck period at the age of three. Then, at thirteen, twenty-three, thirty-three, forty-three, and so on, their major luck period will change each time their age ends with three.
The age at which one starts going through the major luck period varies depending on the individual's birth time. Some start at the age of one, while others start at eight or nine.
There are professional calculation rules for determining the starting age of the major luck period. Due to limited space, I won't elaborate further here.
For instance, a person may go through the "Ren Chen" major luck period for ten years, then the "Gui Si" major luck period for the next ten years, followed by the "Jia Wu" major luck period, and so on.

The term "major luck period" itself has no inherent good or bad meaning. Whether a particular major luck period is good or bad depends on the individual's situation during that stage. We might say this major luck period is good, or this one is not so good, or it is average.
When analyzing the eight characters, we mention the major luck period, saying that during this ten-year period, you are going through a certain major luck period, which is favorable for your fate and brings good fortune.
For example, if a person's fate favors water and wood, and they are currently going through the "Ren Yin" major luck period for ten years, the overall fortune during these ten years is generally good. Even if the fortune in a particular year is not very good, it will not be too bad. However, if they go through the "Bing Shen" major luck period for ten years, the overall fortune during this period may not be very good. Even if the fortune in a particular year is better, it will not be significantly improved.
In summary, everyone must go through the major luck period. The difference lies in the starting age of the major luck period and the timing of its transition.
Going through the major luck period simply means that a new ten-year period of fortune is beginning. Whether this new ten-year period brings good or bad fortune depends on whether the current major luck period is favorable.