How can we consider the impact of local events as a simple sub-part of a validation process when a single event can make a destination unfeasible or prohibitive? If a Grand Prix or a major festival saturates everything, like the Dour festival for a small town, it is a total exclusion condition, not a detail to manage. The tolerance threshold is quickly reached when accommodation triples in price and transportation is blocked. Before committing, one must check if there is an event that can ruin everything, it is the fail-safe of planning.