Men!
Adam decided to talk to God one day and asked for a companion. He was all alone and all the animals were created in pairs. God considered Adam's request and granted it. He asked Adam how this 'woman' had to be. Adam said: "She must be good in householding, the looks of sharon Stone, never have a headache and never complains.God looks a little troubled and answered: "This is gonna cost you at least a arm and two legs."
Adam thought for a while and then he asked what he could get for a rib. So God gave Eve to Adam. He called him over and bestowed upon him 20 years of normal sex life. Adam was horrified! Only 20 years of normal sex life? But the Lord was very adamant - that was all he could have.
So God decided to make issues to the rest of his kingdom. First called the monkey and gave him 20 years. "But I don't need 20 years" he protested, "ten is plenty for me." Adam spoke up eagerly "Can I have the other ten?" the monkey graciously agreed.
Then the Lord called the lion and gave him 20 years; and the lion, like the monkey, wanted only ten. Again Adam spoke up "Can I have the other ten?" the lion said of course he could.
Then came the donkey and he was given 20 years - but, like the others, ten was sufficient. And again adam pleaded; "Can I have the other ten?"
Which explains why man has 20 years of normal sex life - ten years of monkeying around - ten years of lion about it - and ten years of making an ass of himself.