A reader's emotions can be sparked with few words. That's the power of dialogue.
Our instinct as human beings is to provide answers, to ease tension. As writers our job is the opposite, to create tension and not dispel it immediately.
A writer writes what other people only think.
To create tension, dialogue needs to be stretched out. That is, characters should not be immediately responsive.
Dialogue is a lean language in which every word counts.
Dialogue, contrary to popular view, is not a recording of actual speech; it is a semblance of speech, an invented language of exchanges that build in tempo or content toward climaxes.