This summary provides an overview of common errors in Next.js, their causes, and resolutions. The most frequently encountered error is related to accessing browser-specific objects directly in page components, which can be resolved by using React's `useEffect` hook or the dynamic import feature with `ssr` set to false. Another common issue arises when working with middleware in Next.js, typically due to an incorrect server host URL specification, which can be fixed by adding the hostname to the server configuration file. Additionally, errors related to server-side modules like `fs`, module not found, and CORS issues are discussed, along with their respective resolutions. The article emphasizes the importance of using a monitoring tool like Sentry to track the application's state and performance in real-time, providing valuable insights for optimization and reliability improvement.