Think of what is under something rather than what is on top. A wall stands because of the ground it was set into; a claim stands because of what it was set on. In both cases you cannot see the base once the thing is built — you only find out how good it was when weight is put on it.
「底下那一塊」，而不是上面看得到的部分。一面牆能立著，靠的是它嵌進去的地面。一個說法能成立，靠的是它站在什麼上面。兩種情況有個共同點：東西蓋好以後，底下就看不見了。要等到有重量壓上去，才知道當初打得穩不穩。ground 這個字同時是「地面」也是「依據」，兩個意思都從這裡長出來。