The results presented in the paper have significant implications for the design of online auction mechanisms and other practical applications of optimal stopping theory. By characterizing sharp prophet inequalities for single threshold stopping rules, the paper offers a systematic approach to evaluating the performance of stopping rules in sequential decision-making problems. This can be particularly valuable in online auctions where sellers need to determine optimal pricing strategies to maximize revenue while facing uncertainty about buyers' valuations. The game-theoretic framework developed in the paper can help in designing efficient auction mechanisms, setting appropriate reserve prices, and improving overall auction outcomes. Additionally, the insights from the paper can be applied to various other domains such as inventory management, resource allocation, and strategic decision-making in dynamic environments.