Your birth chart is fixed; the sky right now moves every day.
The birth chart you've learned so far is a photo taken of the sky at the moment you were born. It's a fixed map showing who you are, and it never changes for life. But the planets in the sky keep moving even right now, this very moment. A planet today passing over some spot in your birth chart — that's called a transit.
Here's an analogy. Your birth chart is a fixed stage set, and a transit is a spotlight passing over it. Which stage the light shines on decides which area lights up brightly in your life during that stretch. So it's true that even though your signs stay the same, the mood of your luck differs from stretch to stretch. Same person, but some years flow smoothly and some years feel stuck — this is why.
Among the many transits, the two that most shape life's rhythm are Jupiter and Saturn. A Jupiter transit moves about one sign a year, scattering expansion, opportunity, and luck. When Jupiter passes over an important spot in your chart, it's a stretch of new doors opening and widening. A Saturn transit, on the other hand, moves slowly, about one sign every two and a half years, and asks for testing, sorting out, and maturing. When Saturn passes, it's hard, but that's exactly the stretch where your pillars grow solid.
So just like Luck Pillars and Annual Pillars in BaZi, astrology also reads 'what stretch am I in right now' through transits. What matters is that this isn't a scorecard meant to scare you with "this year scores this many points". It's just right to use it as a compass for knowing the flow and preparing — grabbing opportunities during a Jupiter stretch, and not overreaching but building your fundamentals during a Saturn stretch.
This content is for reference and entertainment, based on traditional Chinese metaphysics and astrology.