Read the following fable by Aesop.
The Fox and the Goat
Once upon a time, a fox was out walking in the woods. He did not see a well in the ground ahead, and he fell right into it. It was too deep for him to climb out. After several hours passed, a goat came walking by. The goat was feeling thirsty and saw the fox in the well.
"How's the water down there?" asked the goat.
"Why, hello, Goat," said the fox. "The water tastes great. Why don't you come in and have a sip?"
The goat jumped into the well and leaned down to start drinking. Quickly, the fox leaped onto the goat's back and used her horns to spring up and out of the well.
"Oh no!" said the goat. "Now I'm stuck down here. Please help me!"
But the fox only said, "That was your mistake." And he ran off into the woods.
What is the main theme or lesson of the fable?