Why is this the answer?

The answer is anchor because this heavy tool is exactly what sailors use to make their big ship move or stay put on the water. This fun riddle is giving us great clues about the two most important jobs an anchor does for any boat or ship. Imagine you are sailing a big boat out on a giant ocean or a big lake. You cannot just use brakes to stop like a car. If you just turn off the motor, the wind and the waves will still push the boat around, and you will drift away from where you want to be. To stop safely, you need a special, very heavy tool that will hold the ship in place. That tool is the anchor. Let us look at the first line of the riddle: "Come up and let us go." When the boat is stopped and everyone is ready to leave for a new adventure, the sailors use a strong chain or rope to pull the anchor all the way back up out of the water. The anchor is a huge piece of metal, so pulling it up is a lot of work. Once the anchor is safely on the ship deck, the boat is free. The words "Come up" mean the anchor is being lifted, and "let us go" means the boat can finally start sailing to its next exciting spot. Now look at the second part of the riddle: "Go down and here we stay." This happens when the captain decides the boat has reached the perfect place to stop. The sailors drop the anchor over the side of the ship, and it sinks deep down to the bottom of the water. The anchor has sharp points that dig into the sand or mud on the floor. When it digs in, it grips the bottom so tightly that it holds the massive ship in that one spot. This keeps the boat from floating away with the waves or the current. The words "Go down" mean the anchor is dropped, and "here we stay" means the boat is safely parked and will not drift away while everyone rests or explores. An anchor is an essential piece of equipment for a boat. It tells the story of starting a trip and taking a break, which is exactly what the riddle describes. It is a clever way to talk about a simple object that has a big, important job for every sailor.