Once, people in a city invited Mullah Nasrudin to lecture on Friday. As he climbed the pulpit, he saw that people were not very excited about his presence.
So he asked, "Do you know what I'm going to talk about today?", And people replied, "No!", then he replied: "So I have no desire to talk about a subject that you have no idea" and left.
On the next day, people were curious about what the subject would be and asked him to lecture again, and when he asked them if they knew what the topic would be, they replied: "Yes!" And Mullah Nasrudin replied: "Since you know what I’m going to talk about, I don’t need to lecture" and left.
Now, people were extremely perplexed. So they came up with a plan to finally find out what the lecture was about, and they invited him again.
When he climbed the pulpit, he asked them, "Do you know what I'm going to talk about today?" So half of those present answered yes, and the other half replied that they did not. Then Mullah Nasrudin said to them, "The ones who know explain to those who doesn't," and left.