Odison, It happens all the time, at least on Delta. So many folks carry on larger items, as they do not want to check bags, so they run out of room, and the folks that board last are actually forced to check their carryon. I was asked on my last fight, and refused.....I said, no way, all my good stuff is in this. ( my cute clothes !! ) By the way, we are talking about the carryon's that go in the space department above, not underseat.