Why is it important to avoid duplicating state?

Because duplicated state = a source of bugs. Always.

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#What happens when you duplicate:

• You change one value and forget the other
• The UI shows one thing while the logic thinks another
• It's unclear which of the copies is "the real one"
• Manual synchronization becomes necessary
• Bugs happen "seemingly at random"

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#Example:

You store a products list and a separate filteredProducts list. Then you update products, but forget to update filteredProducts - the screen shows stale data.

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#How to avoid it:

• Use derived state whenever something can be computed
• Keep a single source of truth
• Never store a "copy for convenience" without a good reason

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Conclusion: Duplicated state is a trap for the mind and for bugs. The fewer places where data lives, the cleaner, simpler, and more reliable everything works.