这个故事的主要内容是什么?

这个故事的主要内容是什么?
One day,a farmer was walking along a road with his son Thomas.The father said to his son,“Look!There’s a horseshoe.Pick it up and put it into your bag.” Thomas said,“It is not worth(值得) the trouble.” His father said nothing but he picked it up himself.When they got to a nearby town,they had a rest.There the farmer sold the horseshoe and with the few pennies(便士,货币单位) he bought some cherries(樱桃).
The father and the son continued their way.The sun was well up in the sky,and there was not a house or even a tree where they could have a rest.Thomas felt too thirsty to walk on.At this time,his father dropped a cherry on the ground and Thomas picked it up quickly and ate it.After a while,his father dropped another cherry and once again,his son lost no time in picking it up and putting it in his mouth.
And so they went on.The old farmer dropped the cherries and the son picked them up.When Thomas had eaten up all the cherries,his father said to him,“My dear son,if you had bent(弯腰) down early to pick up that horseshoe,it would not have been necessary for you to bend so many times for the cherries.Always remember the lesson that he who does not worry about the little things will find that he cannot do the great things.”