Let we have a horizontal line segment of 1-unit length and at the left edge point of the line segment we have a perpendicular line segment of 1-unit length, i.e., both the line segments are perpendicular to each other. If we make a “staircase” of equal steps from the top of the perpendicular line segment to the right edge point of the horizontal line segment, we find the length of staircase is always 2 units, no matter how small steps we make (see also the photo attached).
But as soon as the staircase becomes a straight line, its length becomes $\sqrt{2}$ (the hypotenuse of the right-angled triangle with adjacent and perpendicular of 1 unit each). I'm confused between the staircase of a large number of steps (steps being too small as if the staircase were a straight line) having length of 2 units and the a straight line there with length of $\sqrt{2}$.