Nasreddin the Psychologist

Once is Enough
A man invited Nasreddin to join him in hunting for mushrooms and to show him which mushrooms are edible.
Nasreddin assured him that all mushrooms are edible.
“But,” said the man, “my mother warned me that some mushrooms are deadly poisonous.”
Nasreddin replied, “That is true. Although all mushrooms are edible, some can be eaten only once.”