provide a brief fact sheet, legal issues, and analysis, include references

Joe advertised his house for sale and Sam came to have a look at it. While there, they haggled and struck a bargain that Sam would purchase the house for $400,000. They shook hands on the deal and Sam went home. That night, while thinking about it, Sam realized that the house wasn't exactly what he wanted, and so the next day he wrote a letter to Joe stating, "I'm writing this note to let you know that I've changed my mind with respect to the purchase of your home for $400,000, and since the contract isn't valid in any case, I don't expect to hear any more of the matter. Sincerely, Sam." Joe sued Sam for breach of contract. Discuss the legal position of the parties, including any defenses available to Sam.