Manager of one
The concept of being a "manager of one" was introduced by 37signals, and is discussed in detail on the signalvvoice page.
Self-oriented professional
The text highlight the following:
"A manager of one is someone who comes up with their own goals and executes them. They don’t need heavy direction".
Be manager of yourself in my experience is a definition of freedom, This does not imply irresponsibility, but rather highlights of the importance of autonomy and self-management.
Additionally, self-awareness is crucial for making informed decisions about where to focus your effort and how to engage effectively.
More action, less speech
"How can you spot these people? Look at their history. Have they been self-sufficient at previous jobs? Have they defined their own role before?"
I see more value on how people act upon certain situation rather than their knowledge or opinions of a knowledge area.
One example: How did they react during that project when no one took the initiative to help? I am not referring to fully resolving the issue. but rather to the level of interest someone showed in engaging with the situation at work.