When you realize the total combos of car key possibilities, you have a decent chance your key would work, too!

Had two GM 3500 cargo vans, one a 2002 Chevy Express, the other a 2001 GMC Savannah. Same vehicle different badges. Noticed the keys were a bit similar and found that the Chevy key could in fact unlock the GMC with some wiggling but not the other way around. It did not work in the ignition lock.

Ignition locks were always better machined - the door locks were the first to get loose enough for “alternative keys”

Eventually a screwdriver works for both.

Back in the 90s, I was on a trip and ended up parked next to a car which had a car alarm that responded to the key fob for my car alarm. It was very disconcerting.

I borrowed my friend's Prius once and accidentally opened the door to the wrong one and got in for a second before slowly realizing things felt off.

Around 2009ish I parked our dark grey Prius next to another dark grey Prius while going to the Beverly Hills Farmers’ Market and when I came back to the car, there was a third dark grey Prius parked next to the two original dark grey Priuses.

They were reproducing!

It's a keyfob, and it didn't open his door when I tried to get in :P