Real dialogue has as much said as there is unsaid, as there is in any real discussion between two (or more) people.
Furious at your father, you may not mention your feelings.
In love with the woman you're speaking to, and she's unaware, you may not mention it.
Dreaming he'll ask you to marry him, it may not come up when you chat, but it's on your mind.
In drama the unsaid is very powerful, and it pulls us into that empty moment.
How do you write the unsaid?
You must know the emotional life of your characters. You must know not only how they feel in a specific moment, but what is the arc of emotions in their story. Often a character's mind wants something - that drives the plot (money, sex, power, an item) and their heart want something as well - (love of a stranger, reconciliation with a loved one, redemption for past failure) and that is what is completely UNSAID.
Specifically, it is unsaid TO the primary object of affection.
Crucial that is IS SAID to a trusted friend, ally, or piece of paper with a voice over.
That's the challenge in the spoken drama, how do you get OUT of the character's head? The friend can be a shoulder to cry on, or the voice of conscience urging action. So that the HEART story can be voiced. But when it comes down to closing the deal, the hero can't do it. They can't say what needs to be said, can't heal the wound, and has a moment of LOSS, an opportunity missed, perhaps eternally, where the loved one moves off. That is the power of the unsaid - the hero has to be facing the abyss of LOSS after a moment where they could have succeeded. Perhaps time and time again. But ultimately that is too unbearable, forcing them to grow - take a chance - and face their heart's desire and finally SAY the UNSAID.
We've seen it a thousand times in love stories and when it works at the end, it's incredible. Sometimes the unsaid is an action and it's the spontaneous passionate kiss - and when the lovers melt into each other - nothing needs to be said, you've shown it.
In an action film - not surprisingly - action has to accompany this moment, and it's often the physical action that has been UN-ACTIONALBE. Can the hero slay the dragon, essentially, after past failures and current narrow escapes where friends and loved ones have been lost in the struggle? The weight of failure resting so squarely on their shoulders that victory seems a distant dream. But the hero never gives up hope, or re-discovers hope, and re-commits to their mission, so that in the final moment, when they do slay the dragon, it carries that same power.
Less is more.
Write the unsaid.