What did Robin Williams, Oscar-winning actor, stand-up comedian, film producer and screenwriter, leave as his main legacy? Was it his prolific productivity in a career that spanned four decades? His irrepressible presence? His frenetic goofiness and wild sense of humor? His humanity and breadth of emotions, from hilarious to depressed and back? From a business strategy point of view, his principal gift to all of us might well be his ability to improvise and think on his feet.