What common mistake do developers make with Cache keys, why does the mistake cause problems, and what is the safer approach?

What common mistake do developers make with Cache keys, why does the mistake cause problems, and what is the safer approach? One recurring problem with cache keys is applying it without understanding the boundary it protects. Caching mutable data forever and never defining when the cached value must be invalidated. In addition, Cache keys should be deterministic, namespaced and specific enough to avoid collisions. Safer engineering approach: keep the responsibility in the correct layer, use the framework's supported API, validate and authorize inputs, avoid hidden side effects, and verify the behavior with tests.