There are two types of followers: active and passive. They are both followers, but for very different reasons. And understanding their differences can help you avoid disappointment and failure.
Active followers do things in response to your requests. They buy your product, read your posts and enter into dialog with you.
Passive followers, in contrast, do very little. They don't buy, or read, or comment. They are on your side in one sense, but you can't count on them to pull your project or business forward.
(Obviously, because you are reading this post, you are an active follower. And I thank you for that.)
My best guess is that roughly 5% of your total followers are actually active. I know from experience and confirmation from friends that this is about right. It seems pessimistic, but it's the truth.
What does it mean for you? Well, if you have 3,000 followers and hope to launch an ebook for sale, don't expect 3,000 copies to sell. Or even 1,500. No, you can expect maybe 150 buyers. Go into it expecting every follower to buy and you'll only experience disappointment. Expect 5%, and you open up the possibility that you might be pleasantly surprised.