Abstract: Many systems look complicated until we ask what stays the same - at both micro and macro scales. At the micro level, exchangeable interactions and local conservation laws simplify PDEs and networks; at the macro level, these invariances organize families of solutions and predict emergent behavior. Then we’ll break symmetry on purpose to see what drives reality: anisotropy in crystal growth and snowflakes, trust biases that trigger information cascades, and more. Symmetry and its selective breaking offer a way to reduce complexity, illuminate mechanisms, and connect fine-scale rules with large-scale patterns across geometry and the applied sciences.