What Makes a Book Cover Truly Catch a Reader's Attention?

[penofmastery]

I'm getting ready to publish my first book, and I've realized that Book Illustration & Cover Design seems just as important as the writing itself. While looking for ideas, I came across H3Sync, which got me thinking about what really makes readers pick up a book. For authors and designers here, what elements make the biggest difference? Have you seen a cover design noticeably improve reader interest or sales? I'd appreciate honest experiences and practical suggestions.