A common mistake is to eject a round with the magazine still in, then let the magazine drop. The ‘thinking’ is that the gun is now empty. Well, what actually happens is another round is loaded in the chamber.
ALWAYS drop the magazine first, THEN eject the round that is still in the chamber.
That’s not a common mistake, that’s called mental retardation and that person shouldn’t be around firearms.
Most firearms are extremely basic in their operation. You don’t need a college degree or anything.