You don't know him.
Jack was a great guy who had to sell his cow to support his poor starving mum, who had real problems. After negotiating long and hard with a disgruntled vietnam vet, he managed to sell the cow for a bag of magic beans. He got home and when his mum found out he didn't get any money for the cow, he got in big trouble.
This is strange because you can't eat money, and you can eat beans. Just goes to show that being hungry can turn you into a crazy person.
The rest of the story makes up an adventure otherwise known as Jack and the Beanstalk.