Why is this the answer?

The answer is sand because this clever riddle uses tricky words to describe something very important that we find all over the world. It is a wonderful puzzle that shows how sand can do many different jobs, both big and small. Let's look at the first part of the riddle: "I build up castles." If you have ever been to the beach or a big sandbox, you know that sand is the perfect material for building amazing, tall castles. You can scoop it up with a pail, pat it down, and mold it to create a whole kingdom right on the shore, complete with towers and moats. Sand helps you create your perfect play castle. Next, the riddle says, "I tear down mountains." This clue is a bit sneakier because it happens over a very long time. Sand is actually tiny, tiny pieces of rock. For millions and millions of years, the wind, rain, and ice slowly break down huge mountains and big rocks into smaller pieces. This slow process is called erosion, and the final result of all that breaking down is the sand you see today. So, in a way, sand is what is left after a mountain has been naturally "torn down." The third clue is, "I make some men blind." Imagine a big gust of wind on a very sandy day. If the sand is very dry, it can fly up into the air and blow into people's eyes. When that happens, it can hurt and make it impossible to see for a short moment until the sand is cleared out. It reminds us that even tiny grains of sand have power. Finally, the riddle says, "I help others to see." This is a super great clue. When sand is melted down with a lot of heat, it turns into glass. We use glass to make clear windows so we can see outside. More importantly, we use it to make lenses for eyeglasses. These special lenses help people with blurry vision see the world clearly, helping students read their books and grown-ups drive safely. So, from simple, small grains, we get a material that helps us build, see, and learn about the world around us. Sand is truly an amazing part of nature.