A hook is not an introduction and not a summary. It is a mechanism that creates a reason to stay, and there are only a handful that reliably work: contradict something the audience believes, state a specific number, name a cost, withhold the subject of a sentence, or admit a failure. Everything else is a variation on one of those.
The reason it dominates short-form is arithmetic rather than fashion. If eighty per cent of an audience leaves in the first two seconds, no improvement to the remainder of the piece can recover them, so the opening has a higher marginal value than the rest of the piece combined. That is unpleasant and it is true.
The failure mode worth naming is the hook that has nothing to do with the piece. It works once, costs the audience’s trust, and trains them to skip the next one — which is why hook quality should be measured by what happens on the following video, not on this one.
What makes a good hook?
A mechanism rather than a tone. Contradict a belief, state a specific number, name a cost, withhold the subject, or admit a failure. "Make it punchy" is not a mechanism and produces variations of the same sentence.
How long is a hook?
In short-form video, the first one to three seconds. In an article, the first sentence. In an email, the subject line. The length is whatever the audience gets before their decision to leave is made.
Why do hooks stop working?
Because a hook disconnected from the piece is a promise not kept, and audiences learn a channel’s reliability quickly. The honest measure of a hook is retention on the next video, not this one.