An example of a good generalised Q&A: What is a NullPointerException, and how do I fix it?
An example of a Q&A with little to no future value: Here’s my code throwing a NullPointerException. How can I fix it?
Both could’ve been asked by someone who had a real problem, and the answers on either (should) help that specific asker with their actual problem.
The former should help anyone with the same error figure out what’s wrong with their code, except in some rare cases which is specific to some library or tool.
But, for the latter, the accepted answer is little more than “line X is your problem, it should be changed to Y”. The other answer expands a bit on why this is a problem, but it does so in a way which is entirely specific to the asker’s problem. Neither answer is likely to help anyone else. And the question itself isn’t likely to convince someone they’ll get an answer to their similar question there.
As humans, we’d naturally tend more towards the latter for both questions and answers, i.e. focusing on the specific problem instead of trying to create something a bit general. This tendency is something we’ll need to actively fight against if we want Q&A’s more like the former than than the latter.
In conclusion, the selling point should be “get your question answered here … while building a repository of knowledge”. Real questions about real problems, but under the filter of building a repository.