It happens on every second question I try to answer: The question is unclear but the user does not respond.
Why? The usual reason is that the user asking a question seems to leave. Probably to come back later and check if there is any answer.
But on Stack Overflow that doesn't always work so well since there are very often comments asking for clarification.
And if the clarification is not provided, the question gets closed, gets ignored and/or downvoted.
That is really a pity since the first few minutes is the time when a question gets the most attention - especially on Stack Overflow where we have thousands of questions every day and every few seconds a new one. People move on very quickly to the next.
Can we please add a hint telling the user to stay put for at least a few minutes?!
Maybe in the question form, or when taking the tour, or by an online indicating icon visible in the question or at least when closing the browser tab containing the question.
We could tell the user something like @ThinkingStiff suggested:
Things happen quickly on Stack Overflow. Expect comments requesting clarification shortly. Editing your question to satisfy these comments can help get your question answered more accurately.
I think this would also really help in reducing the flood of questions being pushed in the review queue every day.