“But then, in the waning moments of the show, Robin conjures up an exchange between himself and Zak that is essentially un-invent-able: It’s funny, but also achingly sincere and unexpectedly poignant. It’s a rare expression of openness from a performer who was more comfortable with his audience at arm’s length.” In this interactive feature, Dave Itzkoff breaks down his favorite bit from Williams’s now-famous 1986 “A Night at the Met.”