I am sitting on a beach on this hot summer day and watching two children,a  boy and a girl,playing in the sand.They are working hard at building a sandcastle .Just when they are successful, a big wave comes along and puts it down. I think the children may cry because all their hard work turns to nothing, but they surprise me. They run up away from the water, hand in hand, and sit down to build another one. They really teach me a lesson. We can't always be successful.Being sad is doing no good.What we need to do is to start again, hand in hand with our friends. What's the main idea of the passage?
Friends are always there with you Children know more about life. All of us want to be successful. Starting again is the best way.