A couple of years ago, I was on my way to Stapleford aerodrome. As is the norm these days, my GPS was programmed with the destination and I was happily following the magenta line, noting that I would arrive in plenty of time for a coffee before my next activity.
Then it happened. My trusty portable Garmin froze. And I mean froze as nothing I could do would persuade it to reset; in fact, it wouldn't even switch off and the screen showed my last position and time. I did have a back up GPS, but that was in the luggage compartment. However, as I wasn't very familiar with the destination area, I'd taken the precaution of preparing a paper map of the final part of the route. Not something I would normally bothered to have done, but rather fortunate that I'd done so on the day my GPS decided to fail.
Perhaps I should mention at this stage that I wasn't flying, I was in my trusty Teutonic tourer and the GPS froze just after leaving the M25. But software is software and my problem could just have easily have occurred in an aircraft.
(I suspect the reason for the failure was due to some lorry driver with a GPS jammer as it happened as I passed a lorry park. I've had a couple of other brief failures when overtaking foreign HGVs on motorways....)