Sometimes, especially if we're writing in a singular POV of one character, we writers have a particular challenge in front of us. There are so many activities and actions and things that can happen "off stage," so to speak, that don't occur in the presence of our main character. And sometimes, we have to find creative ways either to let that MC witness the action first-hand, or to hear about it second-hand in a realistic way. It can't seem too contrived or manipulated.
For instance - I finished a novel last week (yay, me!) in which the last few scenes contained crucial moments that the MC didn't witness, herself. She had left the area, leaving these other characters behind. But that didn't mean the characters remained frozen, stagnant. Things happened while the MC was gone. And it took some hard thinking and planning on my part, to determine which information she found out and when. And how. I played with it, tested some possibilities, and things finally clicked, fell into place.
But the interesting thing was, in my brainstorming, I had to do something drastic. I had to crawl inside those other characters' mindsets, find out exactly what they experienced that evening--even though it would never be shown in its entirety to the reader in an actual scene. Only the important bits and pieces would be revealed later to the main character in hindsight. But in order for the timeline to work, and for the emotional levels to ring true by the end, it was important for me to get inside those minor characters and live out their actions, anyway.
As writers, we need to always keep in mind that sometimes, what happens behind closed doors, even if it's never revealed it its entirety, is every bit as important as what happens out in the open.