What are the qualities of a great question?

Question

After providing an answer to this recent site-favorite question, I got to wondering about what makes some questions so much more popular than others. As of this writing, we have 14 questions with at least 50 upvotes, two of which have more than 125. This is excellent for the site and great for the askers. We all want to have questions deserving of this kind of attention, especially when they attract a greater number of (hopefully) high-quality answers.

So, what qualities of a question make it great?

Answer 1

The secret to writing a good question is very similar to the secret of writing a good book, or article, or similar. Catch attention, hold it, and direct it.

Catch people's attention with a good title. This should describe what the question is. If it can be humorous, so much the better, but it is very important that the title is clear and easily understandable. It's the first thing people see of your question and the major deciding factor in whether or not people click on it.

Holding attention is the prerogative of your question body. You should be interesting and relatable: as HDE says, if your question is about some highly specialised area of special additional nuclear relativity (is that even a thing?) then most people will give up thinking that they couldn't possibly answer it. Similarly, badly-written questions often get on people's nerves: a few grammar or spelling mistakes here and there are perfectly forgivable, but if it's so bad that it takes effort to read the post, I'll leave about two seconds after downvoting.

Your question body also needs to direct attention. Many good questions have several aspects to them, and without direction the answers would be varied in the topics they talk about. If you're looking for answers on one specific bit, you need to be able to tell people what that bit is. Directing attention is also about making sure that people know your question is on-topic, not too broad, and all the rest of that.

There is also, to some extent, luck involved: unless you're a very good sociologist who can predict what people will react to next (in which case, why are you not employed in advertising?), you will never know if your question will be the next big one or not.

Answer 2

^{This is along the lines of the points discussed in https://physics.meta.stackexchange.com/questions/6303/the-secret-to-getting-a-massive-reputation-is on Physics Stack Exchange.}

Simplicity and straightforwardness

There's sometimes a difference between asking a great question and asking a question everybody can identify with. I could come up with an awesome idea involving ocean currents, but if answering it involves detailed knowledge of fluid dynamics¹ because it's so technical, many people will pass it by. If people can't understand it or relate to it - or if the key is buried in a mountain of text - people will pass it by.

People should be able to read the title, think, "Yes, that's an interesting idea!" and understand everything else from the body, because it rests on common knowledge.

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^{1Which I don't, by the way, have.}

Answer 3

I think this question:

what qualities of a question make it great?

Has a different answer than the answer to:

...what makes some questions so much more popular than others

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I am going to focus on what makes questions popular. Popular questions not only catch attention and keep it as @ArtOfCode stated, they are also interesting to a broad audience as @HDE226868 seems to be suggesting. They create a curiosity that makes one not only wonder what the actual question is, but what the answers are. Sometimes this is created by references to pop-culture or by humorous titles, and sometimes its because its a question everyone can relate too - but most people have never thought about.

Once the question is read, a popular question usually has border-line "too broad" criteria that means everybody could put in a little bit different perspective or focus on a little bit different area. It is also usually about a topic that nearly everyone is equally proficient at and comfortable with - they can't be told "You are wrong" by the "experts", even if there were any. People are excited with the idea, or with the idea of the answers, and they up-vote, or comment, or even add their own answer more readily than they would have otherwise.

This is what makes questions fun to read and answer, but they are not always useful, which is what I think is the main difference between a "great" question, and a "popular" question:

Great questions produce useful questions/answers, but aren't always popular, while Popular questions produce fun questions/answers, but aren't always great