The author argues against testing multiple design options simultaneously, emphasizing that it often leads to unclear outcomes and muddled results. When testing two designs, you might find that aspects of both are appealing, but that doesn't provide a definitive winner. Instead, it complicates the decision-making process and can lead to the discovery of a third, better option that wasn’t even considered. A major concern is that testing with the same participants can lead to biased results. Users might carry knowledge from one version to the next, skewing their preferences based on familiarity rather than the design's effectiveness. Moreover, comparative tests demand significantly more participants—up to three times as many—to ensure statistical validity, making the process more resource-intensive without guaranteed benefits. The author recommends a more streamlined approach: focus on creating one solid design, identify its weaknesses through user feedback, and iterate accordingly. By doing so, designers can achieve better outcomes with less effort, moving away from the pitfalls of simultaneous testing.