Recent research on the decline in the paper disruption index (D-index) has sparked heated debates among scholars and garnered significant attention from policymakers and research institution leaders globally. To bridge the gap between policymakers' interest and scholars' skepticism about the D-index, we present this article summarizing key insights from our eight-year investigation, including interviews with scientists across nine disciplines and an analysis of 41 million papers over six decades. Our work confirms the decline in disruptive papers, addresses relevant technical concerns, and makes several original contributions: we clarify that the D-index measures how new ideas render old ones obsolete, suggesting 'Displacing' as an alternative interpretation for 'D'; we show that federal funding agencies like the NIH and NSF are less likely to support disruptive research; and we introduce the 'principle of functional equivalence' to explain the origins of recombining and displacing mechanisms in science, stressing that not all innovation problems are combinatorial, and challenging the belief that AI is the mature solution to scientific innovation. This article aims to promote broader and more accurate use of the D-index in research evaluation and to inspire new funding mechanisms for scientific breakthroughs.