Have you ever read a book or watched a movie which seemed to believe that its plot elements were more impressive or groundbreaking than they really were? Almost as if the story expected you to get up and clap for its clearly epic and climactic moments? Well, there is a reason for this, and it seems to be a very common pitfall which writers like to run into with open arms. It's all about set up and payoff. When you world build at the beginning of your narrative, you set up expectations. You lay standards for the characters, plot beats, and world all around to react to. The opening chapters, episodes, or scenes of your story will lay the groundwork for what is normal and commonplace, as opposed to what is daring or unexpected in your world. For example, if early on you mention how incredibly rare it is and drastic for an officer of the law to use deadly force against a suspect, and then later you show a policeman shoot and kill somebody, perhaps without need, that action now has weight and gravitas to it. By acknowledging how your world works in the micro, the day-to-day normal action, you then create room for precedent in the macro, the overall function of the world and its inhabitants. This goes back to my previous writing tip about actions and consequences. Because of the way in which you set up the foundations of your world, you now have room to move forward and bend and break those foundations as you see fit in order to create a fascinating story.
In contrast, think now of that awful story you began with, in which the supposedly ground breaking moment is undercut by the fact that, in this world, what just happened really wasn't all that impressive. If police brutality is common in your world, then a sudden such act is practically meaningless in the long run. People read stories in part in order to be wowed, but that only works if you give them room to feel that way.