I think this is why trains and airplanes tend to be delayed so much. It is much better to be late than to leave early. A train that's late will usually still eventually arrive.
a) you're in some weird bus terminal and 60 minutes before the flight the bus is starting to board to take passengers to the plane which is not close b) you're a 15 minute walk and 15 minutes security line away from that cluster of restaurants you decided not to stop at