The Ropshitzer Rebbe was famous for his sense of humor.
Once one of his followers asked him, “What is the reason for your custom to dress in only white cotton clothes?”
The Ropshitzer Rebbe said, “I cannot reveal this to you now. You must first prepare yourself. Immerse yourself in the ritual bath eighteen times every day. After three weeks come to me and I will reveal the reason to you.”
The follower did exactly as the Rebbe ordered, and after three weeks time he proudly went to the Rebbe.
“I did all that you asked,” said the follower. “Please reveal to me the secret.”
The Rebbe said, “Because it is cheaper.”
The follower was confounded: “What? Because it’s cheaper? Why did I have to immerse eighteen times a day for three weeks? Why couldn’t you just tell me?”
The Rebbe answered, “If I would have just told you, then you would have just told someone else, and he would have told someone else, and so on…. And before you know it the price would go up.”