At what fraction of your walking speed must the person in front of you be walking in order for you to initiate an overtaking maneuver? 80%? 70%? It certainly depends on how close they are to you and how far you are from your destination. The worst is when they are walking near the threshold fraction but not quite nearly slow enough, such that your own forward progress is noticeably impeded but overtaking would still take too many seconds. It is one thing to initiate a prolonged overtaking on the highway separated by vehicle metal, high velocity, and possibly even separate lanes; a prolonged overtaking in the pedestrian regime is something else quite different.