If theres a common theme in the stories told by Robin Williams friends in the wake of his tragic death yesterday, its of his fundamental sweetness. Actor and comedian Norm MacDonald contributed a remembrance that may be the sweetest Williams story yet, involving a terrified MacDonald about to perform for David Letterman for the first time. It was my first stand-up appearance on Letterman and I had to follow the funniest man in the world. I was on the phone to a friend back home when the funniest man in the world ambled by.