Nobody has a magic lamp which can tell you in advance whether what you say will be effective in persuading an audience.

Nobody has a magic lamp which can tell you in advance whether what you say will be effective in persuading an audience.

没有人有一盏神灯可以提前告诉你，你所说的是否会有效地说服观众。

-- Maurice Saatchi 莫里斯·萨奇