Imagine the best book you've ever read. Entrancing, enlightening, cathartic. You reach the end, and it's ... perfect. Oh hey, a sequel. Wow, the sequel is just as good as the first book. It expands upon it without diminishing the original -- you feel better, more complete for having read it. Wait, is that a third book in the series? Wow, it's even better than the first two! A fourth -- well, maybe you should go to work now, it's Monday, but the book is so good. Calling in sick once won't hurt anything.
Imagine a perfect series of books, published without end, each better than the last, a new one coming out weekly ... daily ... hourly ...