What criteria do you use to understand that you have done your job well?

Good performance in Golang (and in general) can be assessed based on several criteria:

• Code quality: readable, maintainable code with good structure and comments, adherence to Go idioms.
• Performance: solutions are efficient in terms of time and memory, considering language and environment features.
• Testing: coverage with unit and integration tests, stability and predictability of operation.
• Reliability: error handling, fault tolerance, proper resource management.
• Meeting deadlines: completing tasks within agreed timelines without compromising quality.
• Teamwork: communication, code review, helping colleagues.

For example, if you have written a module that reliably works in production, is covered with tests, easily extendable, and does not cause bugs — this is a clear sign of successful work.