It seems when the creator was making the world, he called man aside and bestowed upon him twenty (20) years of normal sex life. Man was horrified: "Only 20 years?" The creator did not budge and that is all he granted him.
Then he called the monkey and gave him 20 years. "I don't need twenty years" said the monkey" ten is plenty. Man spoke up and said "Can't I have the other ten years?" The monkey agreed.
Then the creator called the lion and gave him 20 years. The lion said he needed only 10 years. Again, man asked "Can't I have the other 10 years"? "Of course!” roared the lion.
Then came the donkey. He was given 20 years and like the others said 10 years was all he needed. Man asked again for the spare 10 years and again received them.
This explains why man has 20 years of normal sex life, 10 years of monkeying around, 10 years of lion about it, and 10 years of making an a$$ of himself.