You're right....I find that coming up with a provocative but not click-baity, succinct title is sometimes tougher than writing the article was.
One thing I try to avoid (and this is going to come across as criticism given that your title to this article does it) doing is the "Six reasons why..." or "Five things to know about..." title. My issue is that EVERYBODY does it now no matter what the topic. My view is that it comes across as cliché.
That said, if it works to pull in readers, who am I to judge? (For the record, it wasn't the "5 Hidden Title Sins..." that prompted me to read your valuable article. It was that your article spoke to an aspect of writing that I've had a bit of difficulty with.)