You can get hired for a job position without being the most intelligent one. But you can get fired without being the dumbest one as well. Getting fired can even be easier than getting hired even was. To get hired, you have to send your resume, get approved, get called into an interview, ace it, and maybe go through even more interviews. Then, finally, after all that effort, you get the job. On the other hand, to get fired, you just need one dumb thing, and that can be reason enough for your job to no longer be yours.
So, if getting fired is that easy, does that mean that everyone could lose their job over one mistake? Well, it depends, but mainly, yes. Especially if the mistake is actually harmful to either the company or your superiors. You have to remember that, as an employee, you are just one more person who works in favor of the company. Your job description also includes being useful, being important for the company, not the reason that damages it. So, if by any means you dumb act or bad day, it's actually harmful to the company, its production, or any of the hired people who work for said company, then you can count on the fact that you will, in fact, get fired. And, unfortunately, there's nothing you can do about it, as it is justified.
I'm sure that every employee who has worked for a while at a company knows at least one story about a person who got fired from the job due to a dumb mistake. Sometimes is something extremely dumb that can even be not able to be understood by other people. And everyone just thinks, "Why did they do that?" But well, those things happen, and we have to just deal with it. If you want to know more about this kind of story, I would suggest checking the thread below.