the.com/ground floor

means The earliest, entry-level stage of a venture or organization — before growth adds the layers (and risk) that come later.

from Literal in origin: the storey of a building level with the street, as opposed to upper floors reached by stairs. The figurative use — 'get in on the ground floor' of an investment or company — emerged from 19th-century American business slang, likening a new venture to a building you join before it's built upward; the lower the floor, the earlier and cheaper the entry, with everything above representing growth (and everyone arriving later paying more, climbing further, and standing on shakier ground).