Habit can make you a victim as well. I once successfully got on SAN-DTW when my routing was SAN-MSP-DTW on PMNW. The SAN-MSP at 14:00 was reliably and always at gate 24 at SAN, so I plopped myself there as usual, GA made an announcement about 13:30 apologizing for a delay and I figured since the plane wasn't at the gate yet we'd be 10-20 behind. Apparently the announcement was for the outbound to DTW which was originally supposed to be arriving around 11:30 and turning right back. I marched up still suspecting nothing and not reading the board, scanner buzzed, GA called the actual MSP gate which had just pushed out of gate 25, but she had seats and after inquiring as to my final of DTW she put me on there. I did get full Y credit and extra EQM for the flight so I came out ahead in miles and in time with the direct but it was all entirely unintentional as I was just in my usual habit.