You have made it very clear that the specific meaning of the words "building a wall has a foothold" in building a house. Of course, this time-honored brand can't fully explain the methods and contents of modern building construction, because in the past, houses were basically built on brick foundations, and concrete beams were generally not poured. I thought you just had to understand it as 1, demolishing the house, digging the foundation on the 2nd, and hitting the wall foundation on the 3rd, symbolically hitting a little wall.
For reference! !