It happens because passengers will insist, even after being advised their hand baggage is too large and does not fit into the gauge, that they must take it on board and will not pay to check another bag into the hold ! We as groundstaff who check in flights and deal with passengers do try very hard to do our jobs properly and do give a "monkeys" ! Unfortunately we have to deal with some very interesting members of the travelling public who really do not give a "monkeys" !!