Originally answered Oct 12, 2017
Good leaders are pleased to see this. They benefit from it, and work to keep the employee challenged. They seek opportunities for the employee to advance, even though that may mean losing the employee’s direct contributions. The best leaders are proud to follow the ensuing careers of their protégés.
Bad leaders are threatened by this. They are afraid of being made to look bad in comparison. They will look for ways to marginalize the employee, or get them to leave.
For more, see Lessons in Leadership.