Cos they don't actually, if you do something like that, say you put plus five, minus five and then sit down and , you're the one that plus three and minus three  you don't actually lose marks doing something wrong, you cannot be penalised for doing it wrong, you can only gain credit for doing something right, because they'll, give you five marks to doing that bit right and then knock three off for doing something else wrong, they, they would never give you penalty marks, they will only credit for doing things right, but so often it's quite like  down as you want, you can't .