Even if you feel like you make stupid mistakes at your job, I am almost certain that you haven't made as many stupid mistakes as the people who have gotten fired less than 24 hours after their first day of work.
The first year of a new job can be stressful. You know that if anything really bad happens to the company, you're going to be the first one to go. All the stuff they told you in the interview about how the company is growing and successful could be patently untrue, and if you aren't able to figure that out before you accept the job, you very well might be signing up to be on the cutting room table within a few short months of getting hired.
If you get hired at a good company, they will understand you won't be perfect at your brand-new job after 3 months. Every employee makes mistakes, and a good manager will guide you rather than reprimand you too harshly for normal mistakes. That said, you should have a solid grasp of your job's daily duties and responsibilities by 3 months in. Your boss shouldn't have to tell you to put on your safety equipment or remind you to schedule 5 newsletters per day if those are basic duties in your job description. Heck, you should know the basic duties of your job before you even walk in the door on day one, because they were probably listed on the job application or discussed in the interview!
In your first week at a new job, you have to mess up pretty badly to get fired. The people in this story got fired almost immediately after getting hired in most of the cases; I 100% understand why.