Why can't you people take your assigned seats?

Listen up, Vacation Warriors!

When the GA announces it's going to be a full flight, and this is not Southwest, it means take your assigned seat.  That means if your boarding pass says "12E", do not sit in 12F, and then when the 12F occupant gets there don't go to the back of the plane to look for another window seat.

It means don't take any two seats together because you can't be bothered to pull out your boarding pass to check which are actually assigned to you, and if you have window and middle, don't take window and aisle and spread out hoping that the aisle will magically stay unassigned.

Thank you.