Why is faces 3D model broken when scale?

Scaling a 3D model can break its faces mainly due to non-uniform scaling (distorting vertex normals or UV maps) or non-manifold geometry (overlapping edges/faces) that can’t maintain structure. Non-uniform scaling messes up how light interacts with faces (normals) or how textures wrap around (UVs), leading to visual or structural issues. Non-manifold shapes—like models with gaps or duplicate faces—fall apart because the software can’t calculate the new form correctly. To fix this, try applying the model’s scale first (e.g., "Apply Scale" in Blender) or use mesh analysis tools to repair non-manifold edges before scaling.