Booker T. Washington's observation can be applied posthumously, perhaps with even greater effect. How better to determine the quality of an individual than with the entirety of that person's life's work? Better still, classics are by definition old, out of copyright, and therefore freely available.
Peter Ferdinand Drucker was an Austrian-born American management consultant, educator, and author, whose writings contributed to the philosophical and practical foundations of the modern business corporation.
"Know Thy Time" is a powerful device in becoming effective. So much so that I have installed the Hours app on my iPad and find tracking my time very effective indeed. The Effective Executive is a seminal self improvement classic. I found many useful lessons in The Effective Executive and highly recommend the book.