Why is this the answer?

The answer is tides because this wonderful riddle is telling us all about the ocean's secret dance. Tides are the way the water in the sea moves up and down along the shore, like the ocean is breathing in and out every day. The first part of the riddle says "In we go, out we go." That perfectly describes the water coming in for high tide and then going back out for low tide. If you have ever been to the beach, you might have noticed how sometimes the water is way up close to the dry sand, and a few hours later, it has moved all the way back, leaving lots of wet sand and tide pools for you to explore. This is the water making its journey "in" and then going "out." It is a constant back and forth. The riddle continues with, "All around and in a row." Tides happen all over the world in all the big oceans, not just at your local beach. They follow a super predictable pattern every single day. Scientists and sailors can actually know exactly when the water will be high and when it will be low for months in advance. It is like the whole ocean is lined up in a row, taking its turn moving in and out. This reliable cycle is very important for sea animals, too, as they need to know when the water will cover their homes. When the riddle says, "Always, always steady flow. When we'll stop, you'll never known," it is talking about how tides are always, always moving. They never stop, even when you are asleep at night. This is because the moon's gravity is the main thing that pulls the water around the Earth, causing the tides to begin with. Since the moon is always up there, using its force to pull on the water, the tides will keep going for millions and millions of years. This steady, non-stop flow is why we can confidently say we will never know when they will stop. The riddle gives us a beautiful and clever way to think about this amazing, powerful natural event that keeps the ocean in constant motion.