I convinced my managers to move away from waterfall to a more iterative process using a financial analogy. Pretty much everyone understands the concept of compound interest as it applies to both debt and savings.

I framed the release of small but functional components as the equivalent of small, regular deposits to a retirement account, where benefits start to accrue immediately and then build upon each other with every "deposit". I framed the holding off of a major project until completion as the accumulation of debt with no payment plan. I also pointed out that, like a sound investment strategy, the "portfolio" of features might require adjustment over time in order to meet objectives under changing circumstances, adding substantial risk to any monolithic project.