jfim explains this well. Airlines want to get you to your destination and will roll you over to another flight if you miss your's. It's happened to me due to tr

jfim explains this well. Airlines want to get you to your destination and will roll you over to another flight if you miss your's. It's happened to me due to traffic jams. And as jfim points out, events like weather or mechanical issues(making departures later than intended) can cause you to miss a layover connection as they tend(not always) to make those razor thin in terms of time.