It feels like a mongoose-bite when your effort is consigned to the dustbin out of the blue. Why not give a "vet for duplicates" button to the poster so that he can self-censor for duplicates?
First of all it is guided in the help center (How do I ask a good question?) to search before asking the question.
Search, and research
Have you thoroughly searched for an answer before asking your question? Sharing your research helps everyone. Tell us what you found and why it didn’t meet your needs. This demonstrates that you’ve taken the time to try to help yourself, it saves us from reiterating obvious answers, and above all, it helps you get a more specific and relevant answer!
Secondly as pointed out in comment, when one writes the question, similar/related questions are listed so-that you can refer them before posting the new one.
Thirdly when you post a question, related questions are filtered in the right panel which you may check.
Fourthly when your question is flagged or voted for closing as duplicate, the system suggest you that "You question may already have an answer...":
By clicking on "That solved my problem" the community user close the question immediately on behalf of you!
And, Btw, you can always cast the close vote on your question to initiate the process.