You're looking for a headline that's an easy upvote. Speaks to the hivemind, surprising or shocking, but not too surprising or shocking, and expands the reader's worldview and/or reinforces their deeply held beliefs, but in a way that isn't blandly repetitive
The post itself must manage to deliver on that promise well enough to avoid downvotes, but doesn't itself matter that much
Fundamentally I must immediatelly think "Wow that's interesting or cool" as soon as I read the title
and then it's all about finding what the audience of a particular site finds interesting or cool
you can even reuse the same content but give the title a different spin or angle to appeal to different audiences
yes once upon a lifetime I have spent far too much time thinking about this stuff. Even got to the point where I could reach the top of HackerNews or Reddit almost at will whenever I wanted to.
That hot streak has largely gone away but primarily because I don't prioritize it anymore and have stopped caring as much. I am content in knowing how to do it and don't feel the need to keep doing it without a larger goal attached.