What is the main problem with using the built-in logger in an application?

The main issue with the built-in logger in Go (log from the standard library) is its limited functionality:

• Lack of logging levels (e.g., DEBUG, INFO, ERROR), which makes message filtering difficult.
• No support for structured logging (key-value), which complicates log analysis.
• Limited options for configuring format and output (e.g., easily switching output to a file or external system).

Because of this, for more complex applications, third-party logging libraries such as zap, logrus, or zerolog are often used, which offer extended capabilities and flexibility.