Job irritation

Why is it ALWAYS that when you do something brilliantly for months you NEVER hear any praise, but as soon as you make a single little mistake you are reprimanded? I think I do a brilliant job with the cash ups every day, I have NEVER made a mistake. For 6 months now. And today I get an email reprimanding me for one little error.
Isn't there something in the Basic Conditions of Employment Act against this sort of thing?!

I'm not sure if people think that we get a share of the company's profit or something, but ever so often we get people accusing us personally of the ridiculously high prices.
"Why do you charge so much?"
"You should give poor students a discount, you make so much money already."
It's note ME dude, I just work here. And definitely don't make money. In fact, I probably earn less than your parents give you every month.
Next time I am going to say:
"If you're concerned about the cost of education, try the cost of ignorance."