Read the following fable by Aesop.
The Fox and the Stork
There once was a clever fox who loved playing tricks. He invited his friend the stork over for dinner one day. When dinner was served, the poor bird saw that the meal was soup served in a flat dish. Try as she might, the stork could not drink the soup with her long, thin beak.
"I'm sorry you aren't enjoying the dinner," the fox said, laughing to himself over his trick.
"Oh, it's no problem at all," the stork said, acting very polite. "You must join me for dinner next time."
Soon the stork invited the fox to her house for dinner. The fox had worked hard all day and was very hungry. But when the stork brought out the food, the fox got a surprise. The dinner was served in tall, narrow jars. With her long beak, the stork had no trouble gobbling up the tasty food. The fox's mouth did not fit in the jar, so he went home hungry.
What is the main theme or lesson of the fable?