The author of this story triggered a preventable application error via a failed call to a third-party API, returning an HTTP 200 status code despite expecting an HTTP 404. This was due to the design of the Twitch API, which returns an empty array in its response even when a user does not exist. The author realized they had written bad code and didn't read the documentation well, but improved their code by adding a check for the length of the data array and sending a message to the chat if a typo occurs. The story highlights the importance of understanding API design, coding defensively around constraints, and using application performance monitoring tools like Sentry to identify gaps in code.