You offer to sell me your Rolex watch that used to belong to Frank Sinatra for $10,000. The contract is written and ifagree to pay you $10,000 tomorrow at 11 am. At 11 am you show up and tell me that you have agreed to sell it to someone else next week for more money. I sue you. I will be able to sue for specific performance since the item is unique. I will only be able to sue for money damages since you have agreed to sell it to someone else for more money. If you have another Rolex that was worn by Elvis Presley, I have to accept that instead. None of the above