Adapa was a guy who lived a very long time ago in ancient Mesopotamia. Mesopotamia is the place where people started writing and where the first cities were built. Adapa was a very smart man who knew a lot of things.
Adapa was also said to be a fisherman and he was one day fishing in the Persian Gulf when a big wind caused some waves that capsized his boat.
The wind was so fierce that it carried him to the heaven and the place where he was a guest was that of Anu, a major god in the Mesopotamian pantheon. Adapa was worried that he had entered the heavenly realm unannounced and that he was going to be punished.
But when he arrived there the gods were impressed with his knowledge and intellect, so they offered him the chance to become immortal. They gave him food and drink known as the "bread of life" and "water of life" that could make a person live forever if they consumed it. But Adapa did not eat or drink those things as he had been forewarned about it by Enki, one of the gods of the river who had helped him before.
So, instead of becoming immortal, Adapa was sent back to earth, where he lived his life as a mortal man just like before. This story was told by ancient people to help explain why human beings can't live forever like gods.