Synthesized answer
The provided passages do not explicitly list the specific evidence the author, Peter F. Drucker, uses to support his claims about executive effectiveness.
However, the passages do state that Drucker "demonstrates the distinctive skill of the executive and offers fresh insights into old and seemingly obvious business situations" by "ranging widely through the annals of business and government" [1]. This suggests his evidence is drawn from a broad study of historical business and government examples. The passages also highlight five essential practices for executive effectiveness that "can, and must, be learned" [1], implying these practices are the result of his observations and analysis.
Synthesized from the book passages below. Chat with the book on Feynman for follow-up.
From the book
Title: The Effective Executive by Peter Ferdinand Drucker Description: What makes an effective executive? The measure of the executive, Peter F. Drucker reminds us, is the ability to "get the right things done." This usually involves doing what other people have overlooked as well as avoiding what is unproductive. Intelligence, imagination, and knowledge may all be wasted in an executive job without the acquired habits of mind that mold them into results. Drucker identifies five practices essential to business effectiveness that can, and must, be learned: Managing time Choosing what to…