In a crowded station, when faced with two possible routes, we tend to follow the person walking ahead of us. Even if they are strangers. Even if their choice increases our travel time. This is the primary discovery of a study published in the Proceedings of the National Academy of Sciences (PNAS). The study emphasizes a mechanism in collective dynamics that has been previously understudied: local imitation among strangers. This mechanism has the potential to produce sequences of consecutive choices, or "decision avalanches", which can have an impact on the safety and fluidity of pedestrian flows. The study, co-authored by Alessandro Gabbana of the University of Ferrara, Ziqi Wang, and Federico Toschi of Eindhoven University of Technology, is based on an analysis of approximately 100,000 individual trajectories collected at Eindhoven Central Station using a high-resolution anonymous tracking system between 2021 and 2024. Using pinpoint measurements and large-scale statistical analyses, the authors discovered that the probability of choosing one of the two paths increases if the person immediately ahead has made the same choice—and that this effect persists even after excluding pairs that can be traced back to social groups (e.g., friends or family). One possible interpretation is that the observed behavior is not a rational choice based on time optimization, but a cognitive shortcut that emerges under conditions of uncertainty and overcrowding. In dynamic and intricate environments, such as a crowded station, the decision to choose the individual immediately in front of you is effortless and readily accessible, even if the information is unreliable. The local imitation mechanism, which reduces individual decision-making effort, can produce unexpected collective effects, such as the amplification of random initial choices and the transformation of them into coherent sequences involving many people, known as "decision avalanches." The researchers also show that these "stranger chases" do not improve individual travel time or overall efficiency; rather, they can create temporary imbalances in flows that impair the system's performance.