1. Why did you make that mistake?
2. Are you stupid?
All of us have been asked these questions at one time or another. This is how they should be translated:
1. You are not perfect and that is wrong.
2. You are stupid.
Warts and all. Some of you may be shocked to see them as they really are: attacks upon someone's self-worth. Both questions are personal attacks in their original form, and are asked as a question because they are "leading questions." This is how I came to these conclusions.
Take the first one. What would be a a valid answer to that question? Think about that. Why does anyone make mistakes? The question is "why" (and sometimes is expressed as "how"), meaning there is intent behind it, like you made this mistake because you wanted it to happen. If you got into a car accident, does a good friend ever ask, "Why?" No. They ask, "What happened?" They assume that you didn't mean to get into an accident because they know accidents are unintentional. Even the most subtle of egos will recognize the first question as an attack, and most of us, unless we have the patience of a saint, will be defensive. But the phrasing of that question bypasses the logical thought, "Wait a minute... that question is not valid!" I have learned to respond either, "why does anyone make mistakes?" or "what kind of response to you expect from such a question?" The person will either apologize or insult you more directly, making their intent known.
The second one is more often used on children, but I have seen used on adults by particularly childish bosses. Thankfully, I have not had a boss like that in a long time; they usually asked the first question, not knowing they were making an attack, but their anger did, and my ego received the message as intended.
No one should ask those two questions, because at the very least, you won't get a satisfactory response, and usually, you'll hurt someone and cause them to react defensively, which will obscure the reasoning that led to the mistake, and it's just a time waster and childish.
If someone makes a mistake, it's best not to get angry and ask, instead something like, "What happened?" or "What can we do so this doesn't happen again?" if the mistake keeps repeating itself.