A wise old man.

[flobadob]

A rich old man is nearing the end of his days and must decide which of his two sons shall receive his estate when he passes away. He knows that neither son will ever share with the other. He calls his sons before him to tell them of his plan. He tells them that they must each go to their own stables and choose their finest horse, and they must then have a race. He tells his sons that whomevers horse finishes in LAST place that son shall inherit his entire estate. The sons each choose their finest horse and take their place at the starting line and the father intructs them to race. Obviously neither son makes much progress as neither wants their horse to win the race. After an hour or so they realise they are getting nowhere but don't know how to resolve the issue as they don't get on. They see a wise old man walking nearby and decide to pose him their dilemma. The wise man gives them his advice at which point they both run straight over to the horses, jump on and take off as fast as they can over the finish line. What advice did the old man give?

[doglady]

They swap horses. It's whichever son's HORSE finishes last, so they both try to win on the other's horse.