Clinical guidelines represent statements that seek to synthesize the best evidence to guide a course of action to improve health outcomes and more cost-effective use of resources. However, even when the evidence is not definitive, comprehensive documents are still needed to guide clinical decision-making. In these circumstances, guidelines are inevitably affected by perceptions of the problem and their possible solutions. From 1998 to 2014, 10 different international guidelines have focused on the aortopathy related to bicuspid aortic valves. Recommended thresholds for intervention started at a cutoff level of 5.5cm in 1998, reached a nadir of 4 to 4.5cm in 2010, and returned to a 5.5cm cutoff level in 2014. During this time, no conclusive objective proof was published to support either an aggressive or conservative strategy. The consequence was that an undefined number of patients underwent surgery (and potential complications thereof) at an earlier disease stage than might have been necessary. This experience might provide a clue as to how guidelines evolve, and provide insight as to how to avoid a similar process in the future.