Why does HN allow duplicate submissions?

HN allows duplicate submissions of stories that haven't had significant attention in about a year. We want good stories to have multiple chances at making the front page.

Our goal is to optimize HN for curiosity and the front page for the best stories, and it's fairly random whether or not a good story gets traction the first time it's posted. If we were anal about disallowing reposts, sure we'd get a more deduplicated submission history, but we'd also end up with a poorer front page. Bad trade.

There are things we're working on to reduce the number of dupes that are appearing. The problem is trickier than it seems, but we'll get there.

I think it's because one person might come up with a more convincing headline than another that causes the post to take off here. If that's the case, the first one to submit shouldn't always win. Also, if multiple threads on the same topic take off at about the same time, mods sometimes merge the two.

Good point, I also noticed URLS that have been already discused, submited again, after couple of weeks. Some duplicity check, would be helpful.

It's getting worse every day and will continue to worsen until submitters start losing points for submitting dupes.