The word 垫底 is formed through a vivid conceptual metaphor rooted in the literal action of placing a cushion or supportive layer at the very bottom of something, such as a lining in a box or a mat under a dish. This concrete image of being the foundational base is extended metaphorically to describe a person or thing occupying the lowest position in a hierarchy or ranking, much like the foundational layer that supports everything above it but is itself at the bottom. Thus, its meaning evolves from a physical action to an abstract state of being last or serving as the baseline.