How answers pick their sources
Generative engines answer in two moves: retrieve candidate sources (heavily search-index-shaped: ranking still matters), then compose with citations, favouring passages that answer the question directly and stand alone, sources whose facts corroborate across the web, clear authorship and recency, and unambiguous structure. Optimisation follows the mechanism: win retrieval with classic SEO, win citation with answer engineering.
The empirical grounding
Published research (Princeton's GEO study most cited) and consistent practitioner testing agree on the levers: quotable statistics and direct answers lift citation likelihood; keyword stuffing measurably hurts it; structure and sourcing beat persuasion tricks.