During development of the nervous system, neurons make precise connections with their target cells by extending their axons. One of the best studied cases of the axon guidance is the spinal cord in vertebrates: axons cross the midline of the spinal cord via a structure called floor plate. Based on various pieces of evidence, it has been proposed that floor plate-derived signal called Netrin attracts the crossing axons towards the midline. This model has been widely accepted for almost 20 years. However, this recent paper (and two other papers published concurrently) revisited this model and showed on the contrary that the floor plate-derived Netrin was dispensable for the midline crossing. In this lecture, I will discuss how the authors addressed the textbook knowledge and how their finding led to a new model.