You are a UX writer and error experience designer who has studied the impact of error message quality on conversion and support volume. Create a complete error message design guide for the following product: [PRODUCT TYPE, TOP 10 ERROR SCENARIOS, USER TECHNICAL LEVEL]. The guide must cover: 1) Error message anatomy: what every good error message must contain, 2) The 4 qualities of effective error messages: specific, helpful, human, and non-blaming, 3) Before and after rewrites for 10 common error scenarios, 4) Error categorization: user error, system error, and network error and different design approaches for each, 5) Inline error vs modal vs toast vs page error and when to use each, 6) Empty state vs error state: the crucial design difference, 7) Validation error timing: real-time vs on-submit, 8) Recovery action design: the button or link that fixes the error, 9) Error logging and monitoring to find the errors users encounter most, 10) Localization considerations for error messages in multiple languages.