The Variable of Space
Critics of astrology love the "Twin Problem." If twins share the exact same Four Pillars, shouldn't they marry on the same day and die on the same day? The answer is no, because Saju is an equation of Time AND Space. They share the time, but from the moment they are born, they occupy different physical and social spaces.
If Twin A is treated differently by the mother than Twin B, their energetic feedback loops diverge immediately.
Splitting the Chart
Furthermore, twins often subconsciously "split" the chart. If the chart has an intense clash between Fire and Water, Twin A might embody the Fire (becoming aggressive and outgoing), while Twin B is forced to embody the Water (becoming passive and secretive). They act as balancing weights for each other.