> This isn't really a React-specific tip, as such anti-patterns often occur in code in general; in this case, React simply points them out more clearly.
Using state to cache values calculated from props (for example in `getInitialState`) often leads to duplication of "source of truth", i.e. where the real data is. Whenever possible, compute values on-the-fly to ensure that they don't get out of sync later on and cause maintenance trouble.