The Need-Driven Expansion Hypothesis (NDEH) offers a grounded framework for understanding why interstellar colonisation might be far rarer than science fiction suggests. Rather than assuming that advanced civilisations will inevitably spread through the stars, NDEH argues that such expansion only occurs when the benefits clearly outweigh the immense costs—particularly those tied to time, distance, and isolation. The model deliberately focuses on scenarios rooted in currently plausible physics and engineering, setting aside speculative technologies like faster-than-light travel or stasis. By examining how practical, psychological, and cultural factors intersect with the limits of space travel, NDEH provides a realistic lens through which to explore the Fermi Paradox and the likely behaviours of spacefaring civilisations.