Read the passage and answer the question.

Once upon a time, four boys lived in the countryside. One boy was very clever, but he did not like books. His name was Good Sense. The other boys were not very clever, but they read every book in the school. When they became grown men, they decided to go out into the world to earn their livelihood.

They left home and came to a forest where they halted for the night. When they woke up in the morning, they found the bones of a lion. Three of them, who had learnt their books well at school, decided to make a lion out of the bones.

Good Sense told them, “A lion is a dangerous animal. It will kill us. Don’t make a lion.” But the three disregarded his advice and started making a lion. Good Sense was very clever. When his friends were busy making the lion, he climbed up a tree to save himself. No sooner had the three young men created the lion and gave it life, than it pounced upon them and ate them up. Good Sense climbed down the tree and went home very sadly.

What advice did Good Sense give his friends?