Open your last post and read only the first line. Then stop, the way a reader actually does. If that line alone wouldn't make you keep going, it didn't make them either, and everything underneath it was written for nobody.
That is the math of social copy, and it is harsher than most advice admits. People scroll past an enormous amount of feed every day, and they decide whether to stop in less time than it took you to type "Excited to share." A caption lives or dies on its first line. Sometimes its first five words. Everything after only gets read if that line earned it.
So write the first line like it is the only thing you are allowed to publish.
The reason most of us don't is that the first line is the hardest sentence to write, so we postpone it and open with throat-clearing instead. "Excited to share..." "As a small business owner, I know that..." "In this post, I'll be breaking down..." None of those are hooks. They are you warming up where the reader can see you, and the reader is gone before you finish stretching.
A first line that works does one of three jobs. It says something unexpected ("I deleted our most popular blog post on purpose"). It names a pain the reader is in right now ("Your captions take an hour and still sound like everyone else's"). Or it opens a loop they have to close ("One word doubled our reply rate, and I almost didn't ship it"). None of them need a hashtag to land.
Then run the delete test, which costs nothing. Write the caption, delete the first sentence, and read what's left. If the post got better, that sentence was throat-clearing, and the line now sitting on top is your real hook. Do it again. Most captions survive losing two sentences off the top. Some survive four. Almost none get worse.
It feels wrong because we draft top to bottom, so the warm-up ends up in the one spot that has to do all the work. You would never send your slowest runner out first and hope the race sorts itself out, but that is the default caption.
And resist making the first line clever for its own sake. Clever ages badly and smells like a copywriter trying to be noticed. What lasts is being first with something true and specific, before the reader's thumb makes the only decision that counts.
Sweat the first line. Write the rest like a reward for the few who stayed, because that is who it's for.