There are a couple routes screenwriters have for delivering information to their audience. There's exposition -- where plot or character is explained through dialogue -- then there are visual or aural descriptions meant to convey emotion. Basically it all boils down to telling or showing, but however its done, every line of dialogue, every scene, and every emotion in a film should have one express purpose: to advance the story. How a screenwriter chooses to reveal the information of their characters and plot has a direct relation to how we experience the tone and atmosphere of a film, and as such, that information (and our emotions about said information) are ripe for manipulation. Take Alex Garland's script for Ex Machina, which he also directed.