I've missed flights before.

About 25% of my flights are "close calls". You just need to have a backup plan always in mind.

p.s. Two years ago, on the night of the first Seder, I misconnected in HKG (thanks to HKG station staff-- some of the worst in the world), so I feel your pain. That one wasn't my fault, so I was especially pissed.

DCA is about the worst, because they like to close the door at T-20 so long as most passengers are on board; even this 1K traveling on an FPASSA fare was scolded for getting to the gate at T-17. I'd complain, but the CoC does have a 20-minute rule, so I just consider it lousy customer service and leave it at that. My other UA stations follow UA's general policy which seems to be between T-5 and T-10 for closing a flight.