Shakespeare wrote a play "The Death of Caesar". It is said that this sentence is Shakespeare's emotion about "The Death of Caesar". In the play, Caesar was assassinated to death by conspirators headed by Brutus. Brutus was Caesar's favorite subordinate. His surface humility and smile confused Caesar. Caesar treated him like his own son and trusted him. But he didn't expect that behind Brutus's smile there was a conspiracy to assassinate him. Before his death, Caesar lamented how Brutus could be among those who killed him. Therefore, Shakespeare said: "Laughter is the root of all evil." The smile here of course refers to a smile that is as sweet as Brutus's, a smile that is secretive and has a conspiracy behind it.