[havkom]

This skill is what differentiates really good developers from not so good developers (that may wrongly believe themselves they are good):

How good are you at reading code, finding out how smaller parts work in a larger system and understanding the context&domain is a large part in how good you are.

Not so good developers, when they are not so good at this, often start blaming the system and people who have worked on it.

Not so good developers may however be able to handle smaller systems (in particular ones written in their favorite tech stack), and this experience leads them to erroneously believe they are good.