Must know principal for cleaning up your code.

Magic numbers are unnamed values in code that lack context about their purpose or origin. Instead of scattering literal values throughout your code, use named data structures like Python's namedtuple to give meaningful names to values. This approach makes code more maintainable, reduces errors when updating values, and clearly documents what each number represents. The example demonstrates refactoring shipping cost calculations from hardcoded numbers to a structured dictionary with named fields for weight limits and fees per destination.