I considered calling this one Accepting Blame, except my general rule is fix the problem, not the blame. Unless you're the problem. Then the blame is yours, too.
When interviewing for a job, generally you are given a list of job duties that you are expected to perform on a routine basis. This is rarely a comprehensive list, but it will cover the minimum expectations of both you and your employer. Meaning, if you can't do these things on a routine basis with a minimum of mistakes and no supervision, you should be fired.
If you are a server at Sonic and can't make change, you should be fired. If you work at a phone bank answering calls all day and regularly forget to turn on your phone or yell at back at frustrated customers, you should be fired. If you data-enter numbers, and you regularly transpose them, you should be fired.
The above paragraph makes the mistake most employees make: it assumes it is your employer's responsibility to remove you. Wrong. It is your responsibility to remove yourself. A person of integrity who agrees to perform certain tasks in exchange for money, who discovers he cannot perform those tasks, should refuse payment and find another job better suited to his skill set. Unfortunately, the workplace is full of lemmings who would rather be told what to do than lionesses who solve problems, especially when that problem is herself.
I do not mean people cannot make mistakes. People are people, competent or not, and everyone has bad days. When those happen, own them, do your best anyway, and expect to have some messes to clean up later. That's normal. But the consistent failure to do the minimum your job requires is unacceptable to everyone: the customer who can take his business elsewhere, your co-workers who have to bail you out while still doing their own jobs, and your boss who's literally paying you to cause problems she doesn't need.
If you make simple mistakes on a regular basis that cause extra work for everyone, you can expect to work in a hostile environment. I recommend accepting responsibility and doing what you need to do to get your act together. If you don't, your boss will do her job and fire you, and you will have only yourself to blame. If you're a lemming, that won't stop you from blaming everyone else anyway.
Push button. Receive bacon.