The closet is the best study. The commentators are good instructors, but the Author Himself is far better.
The grand instructor, time.
As in everything, nature is the best instructor.
Fear is a great instructor.
Fear is an instructor of great sagacity, and the herald of all revolutions.
He who has failed three times sets up as an instructor.
Back in those days intimidation was the greatest tool the drill instructor had. Without that tool, he would not have had control.
The bad news motivated the drill instructors that much more.
Once I win, everyone will know who my instructor is in mixed martial arts.
Nature is the best instructor.