When they understand the difference between software engineering and software development. A senior software developer understands what it means to scale and a

When they understand the difference between software engineering and software development. A senior software developer understands what it means to scale and align software engineers, as a unit or team. This along with understanding that the code is not what matters but rather what the algorithmic design, innovation, invention or discovery that can be done with a particular language or code (or notation in mathematics or music).