Why does the IT book have THE STUPIDEST STRUCTURE?
Why couldn't he just write in a chronologically straightforward fashion, like this movie did? The structure he chose removes all sense of suspense and drama, because you KNOW the Losers survived their childhood encounter with Pennywise, so it reduces HIS threat as the antagonist right there and then.
At least this movie corrected that problem outright, which probably explains why it was so popular and so bankable. And for Chapter 2, I would say that flashbacks to the past are necessary as Pennywise made the Losers forget their ordeal, or PTSD blanked their memories, so they needed to remember, plus we get some more cool encounter scenes.
The book is difficult to follow sometimes, as it goes back and forth all over the place, and I haven't been able to work out the structure yet. Even the journey into the sewer goes back and forth between time periods, and while I suppose King wrote it that way to avoid repetition, it doesn't work as it is.
King really dropped the ball on the writing of this book, but since he was on drugs at the time, it's understandable.