[lo_zamoyski]

Or someone who does both.

1. Only working on greenfield means you don't want to learn from others or have difficulty doing it. Lots of knowledge is expressed in the code you refuse to read and you need humility and patience with your own ignorance.

2. Only reading code is insufficient as you are not only a scholar of the code base, but a maintainer and developer who must extend and adapt it.

Working with a code base is more like a conversation. There's a back and forth, though not symmetrical. (1) is someone who monologues. (2) is an audience member only.