When a Node.js app hangs after a failed database connection, it is usually due to poor error handling around the database connection logic. If the database connection fails and is not properly caught, the app may wait indefinitely for a response that will never arrive, causing it to hang. To fix this, ensure that all database connection attempts are wrapped in `try/catch` blocks, and add appropriate logic to handle failures gracefully, such as logging the error and retrying the connection after a short delay. Using libraries like `retry` can simplify this process by providing automatic retry logic with exponential backoff. Additionally, setting up a circuit breaker pattern can help prevent your app from continually trying to connect to an unresponsive database, which can overload the server. A well-designed error handling and recovery strategy ensures that your Node.js app can handle database failures without hanging or crashing, providing a better experience for users.