In fact, this can't be explained from the perspective of limit. Strictly speaking, 1=0.9 ... is another way to mark 1. We know that 0.9, 0.99, 0.999, 0.9999, 0.99999 go straight ahead. For any number A less than A, we can definitely find an item greater than A, and the limit of this series is 1. So let's assume that a number 0.9 ... is an infinite term in this series. For any number greater than 6599, we write 1 as 0.9 ... Therefore, either 0.9 ... does not exist, or 1=0.9 ... After this regulation, every real number can be expressed by an infinite decimal, so that real numbers can be made.