Marty Sklar had only just graduated from UCLA, and here he was shadowing Walt Disney, his demanding new boss. The fledgling writer was unsure how to make himself useful, but he had a mind to scribble down some of the maxims Disney laced into conversation. “Know your audience.” “Tell one story at a time.” “Wear your guests' shoes.” Long after his mentor's death, Sklar recognized the treasure-trove of wisdom he had started compiling at Walt Disney's elbow in the late 1950s. He distilled it all into "Mickey's Ten Commandments," a widely circulated creed that remains a touchstone in the theme...