If people encounter a title that doesn't fully yield to 300ms of parsing, that causes irritation, which is a good thing. Not good in itself—irritation is a bit painful—but good because it causes the rapid-reflexive subsystem to throw an error and pass control to the slower, reflective system that is able to process more information. That's the system we actually want to get activated. One's it's engaged there's a chance that it will remain engaged, which—this is the hypothesis anyway—will lead to higher-quality thoughts and comments. That's why I say it's good for HN users to have to work a little.
"You won't believe who's giving a way a repo
#2 will shock you"
That kind of title operates even less by intellectual curiosity than the kind I was talking above, so it's even worse for HN. They are the kind we edit and everyone agrees with the edit.