It's all Legacy Code
The truth is that 99% of a professional software engineer’s job is refactoring other people’s code (AKA “Legacy Code”).
Given this fact, an engineer seeking success should study methodologies for working with legacy code.
There are a few methodologies (or tools) that the community has developed that ought to be reviewed:
1. Test-driven development, or TDD
2. Types of automated tests
3. Mocking behaviors where your software interacts with the “outside” world
- third party APIs
- network I/O
- hardware I/O (meatspace)
These methodologies are inherited from physical engineering (mechanical/civil/aeronautical/etc.), and have a track record longer than any of us reading this have been alive.
A software engineer that is deeply-versed in these methodology will be successful in their role as an operator.