"But everyone who hears these words of mine and does not put them into practice is like a foolish man who built his house on sand"
We weren't made to build houses on sand just like we shouldn't place our foundation on people or things. Foundation should be built on the rock by hearing and putting into practice the words of Jesus.
"never, never pin your whole faith on any human being: not if he is the best and wisest in the whole world. There are lots of nice things you can do with sand: but do no try building a house on it." C.S. Lewis
"On Christ the solid rock I stand. All other ground is sinking sand."