Having a slow start to your story can make the reader lose interest early on and risk having them decide to stop reading within the first 50 pages. To avoid this, you'll want to make sure your call-to-action comes early on. The call-to-action is what prompts your protagonist into working toward their main goal. If a protagonist's little brother is kidnapped, that event will be the call-to-action that prompts the protagonist to go out and rescue their sibling. If the call-to-action doesn't appear till page 50, there's a good chance that the first 50 pages of your story are "fluff" chapters (chapters that don't have anything important happening in them) and therefore should be cut. You want your opening chapters to introduce the call-to-action to set your plot into motion.