Yep, that sucks. But on the other hand, overbooking is a thing, so if you buy a ticket without seat selection for a popular flight there's a chance you literally won't be let into the plane you paid for because all the seats are already taken. Happened to me once, I had to agree to a free replacement ticket to a different city in an entirely different European country (Brussels instead of Cologne) and spend about 200€ on a late night taxi to my destination.