I answered this question: Is it possible to free local allocated memory with VirtualFreeEx? but my answer was deleted. The answer is demonstrably correct. Why was it deleted?
Brevity, in and of itself, isn't necessarily a problem for some kinds of answers, but it almost always is when the answer is "yes" or "no", because those answers aren't very helpful to the OP.
When something is known to be in question, which one can definitionally assume to be the case with almost any question posted on the site, a simple "yes" or "no" will almost never be sufficient to provide a trustworthy resolution to the inquiry.
Even in those fairly rare cases where you don't need additional details to implement, use, or understand the answer, the problem is still that you haven't been given enough information to believe it.
When you're saying, "yes", even if you can't link to source material, in order to help the OP know that you're right, you generally need to provide an explanation of what makes it possible to do a thing, or what's incorrect in the assumptions that made you think it wasn't possible.
A simple yes or no doesn't provide the OP with enough information to trust the response - they don't even have any indicators to support the likelihood that you fully understood their question. You probably did, but...
Imagine asking this question in the real world, on the street, say, and someone walking by interjected with a simple, "Yes". You wouldn't buy it unless they explained enough of their reasoning to be compelling.
In my opinion, you could argue that it should have gotten comments requesting more explanation, rather than being deleted, which is a valid discussion, but not that it was useful in its original form.
You could well have phrased this question "Is there any justifiable reason for deleting my demonstrably correct answer?" and we could have answered "yes" to that.
You've given a pedantic but extremely unhelpful answer. If I ask "Is it possible to do X?" it's very clear that I (a) would like to do X (b) can't see how to do X and (c) would like help in doing X or an explanation why it's impossible. To interpret this as a simple yes/no question is to misinterpret the OP.
Feel free to edit the question to ask "Is it possiible to do X? If so, how? If not, why not?".
Answering like you did could be intepreted as sarcastic, and can definitely be interpreted as unhelpful, which is probably why it was deleted.
You say it was demonstrably correct? You should have demonstrated it in your answer. If you don't want to say why, then a comment would be an appropriate place to say "Yes it is, I'll maybe explain later if no-one else does in the meantime."
Despite the fact that the OP asked a "yes or no" question, your reputation and history on SO demonstrate that you were probably perfectly aware of what the OP of that question was really asking (whether they could do X, and if so, how?).
Thus your answer was not an answer to the real question at hand. It was a sarcastic, non-answer. Non-answers get deleted all the time.
Because it is not really an answer, it could have been a comment. Even for questions where a simple 'yes' might be a correct answer, quality standards on Stack Overflow are higher than that. You could have added why the answer is 'Yes', at the very least.
Most likely it was added to the low quality queue for review, or it was directly flagged as not an answer. A moderator then deleted it based on the flags and the general lack of information your answer provided.