Of course, the Dropbox post has a meme-level example of an HNer predicting its popularity :) [0]

That said, it also often happen that you share something and it is not picked up, even though after 10 years I think I can predict what HN loves. Sometimes a repost after 2 days will hit the front page, certainly not always.

[0] https://news.ycombinator.com/item?id=9224