We must pay attention to the basics and lay a solid foundation. What is the eight-character idiom?

Water without a source, tree without roots. Source: water source; root: tree roots. Water without a source, trees without roots. Metaphor for something without foundation.

Without the skin, how can the hair be attached? Yan: where; attached: attached. The skin is gone, where will the hair attach itself? It means that things cannot exist if they lose the basis for their existence.