Everything you know is a lie. It doesn't matter how sure you are about something, I'm now telling you that you are now wrong. The world has been flipped upside down because Nintendo has come out and told everyone that Mario is not a plumber. Not anymore anyway.
According to his new Japanese language profile, Mario doesn't do any plumbing work anymore. Here's a rough translation:
All around sporty, whether it’s tennis or baseball, soccer or car racing, he [Mario] does everything cool. As a matter of fact, he also seems to have worked as a plumber a long time ago...
They can't just decide that Mario isn't a plumber anymore, or speculate that's what he might have done in the past. Mario is built on being the everyman hero, coming from a blue-collar background and proving himself worthy of courting royalty. He's an inspiration to us lowborn plebs all over the world.
In fairness Mario doesn't appear to have done any actual plumbing work for quite some time. He's spent the last 36 years of his life beating up giant gorillas, go-karting, playing tennis, beating up turtles, and other things. While some might snigger and regurgitate some stereotypes of the Italian work ethic, it's clear that Mario will have been sacked from his duties long ago.
Or his plumbing company went out of business due to lack of incoming money. I don't think they accept Mushroom Kingdom coins in the real world.
That's if he was ever a qualified plumber in the first place. I somehow doubt that he's a properly qualified doctor, even if his response to every ailment is to throw antibiotics at them until things go horribly wrong. [Nintendo Japan via Kotaku]