Costello hired Sagan to energy his racing car in a race. Sagan's friend Gideon promised to pay Sagan $3000 if she won the race. Sagan won the race however Gideon refused to pay the $3000. Gideon contended that no lawfully binding contract had been formed for the reason that he had received no consideration from Sagan in exchange for his promise to pay the $3000. Sagan sued Gideon for breach of contract arguing that winning the race was the consideration given in exchange for Gideon's promise to pay the $3000. Explain what rule of law that we have discussed supports Gideon's argument?