In the book, "Extreme Ownership", Jocko Willink states that a group is only as good as their leader. A true leader cannot lead alone, rather, they require a group behind them that is focused on the goal. Also, a leader can only be considered a good leader when their team reaches their goals on a regular basis. 

Willink describes that the leader needs to be modest and realize once they had been incorrect. Possessing mistakes and developing a method to right any errors is fundamental to be a successful leader. Leaders must keep the ego at the door, and their agenda is entirely specialized in their group, they need to ignore their agenda. Willink's perception of a leader that is beneficial to their group as someone who can concentrate purely on the goal and bring the team together to reach that goal. 

This book contains a comprehensive, well detailed summary and key takeaways of the original book by Jocko Willink. It summarizes the book in detail, to help people effectively understand, articulate and imbibe the original work by Willink. This book is not meant to replace the original book but to serve as a companion to it.