People sometimes make the distinction about whether aspects of fiction are “realistic” or not. Generally, I feel fiction doesn’t have to be (it is fiction after all), and that it’s more important that it be “true”.
What I mean is that some aspect of the scene has to be presented truthfully. The reader/audience’s reaction should be “that’s how that character would behave”, “people are like that”, or “that’s what would happen”. It’s about resonance, often on an emotional level. If you (the writer) have achieved that, then the audience will be following you, even if events are not realistic.
It does help, though, if events are also plausible. They don’t need to match how things behave in the “real world”, but they should fit with the way things work in the fictional world that is presented. If a fantasy novel establishes how magic works, then it’s cheating to have it suddenly do something different, and smacks of a writer who has painted themselves into a corner.
Alternatively, you can focus too much on making a scene work on an emotional level, so the audience/reader goes along with it, but later on thinks that something seemed not quite right1.
For an (extended) example, I recently was watching a scene described as a “spies goodbye”. A couple of agents had been captured, their covers were blown2, and their only option was to “retire” from the game and never make contact with their former allies/co-workers. The two are morosely drowning their sorrows in a dimly-lit bar. The waitress brings over a drink, saying it’s a gift from another table. They glance around, and spot one of their (former) colleagues at another table in the corner. This happens several more times, as they realise their whole team are lurking in various parts of the room3. One by one, they make (tearful) eye contact, raise their glasses, then quietly leave.
Emotionally, it hits the mark. It’s fiction, so it doesn’t matter that in the real world this would be a blatant violation of the “cannot make any contact” restriction, but on reflection, it still feels a bit implausible. My main issue is that it breaks one of the cardinal rules of subterfuge: have a reason for being there4.
Is this fixable? A similar effect could be achieved by having the team members nabbing a nearby table and loudly sharing a toast to absent friends—they’re all wearing black (or at least dark colours), anyway, so they’ll give other patrons the impression that they’ve come from a funeral. Far less likely to draw unwanted attention than several people buying drinks for and saluting an otherwise inconspicuous couple. You can still use largely the same camera angles, but without the sense that people are staring at those they supposedly don’t know.
The advantage of being a writer is that any painted corner is escapable. And, if you do it right, you can reinforce other aspects of character/world, without the audience ever realising you were in a pickle to start with.
2 You know the drill—a mission goes wrong, agents have to improvise, “if you are captured, the Agency will disavow any knowledge of your actions (or even existence)”, etc.
3 And clearly want to get them really drunk.
4 It’s been frequently shown that people (only) remember things they focus on. Details that “fit” an expected pattern, that don’t stand out, will likely be forgotten.