I didn't board a "wrong" plane, but I arrived at the gate about 20 minutes before departure time, and saw no one lining up to board the aircraft, so I didn't bother asking why, cuz there are a lot of people sitting in chairs in the waiting area, and so I thought boarding hadn't started yet due to some type of delay, as normally, you'd see a line of people getting to board the plane 20 minutes before gate closes. Well, it turns out that I was the last passenger, and I did NOT hear any announcement making last boarding call, and the status on the TV screen at the gate indicated NOTHING (in fact, no status at all, no mention of boarding, final boarding, delay, etc).

So the aircraft left without me.