Without saying so, we talk a lot about the middle when we discuss the elements of writing. Here are some random thoughts on middle stuff. Today's topic is conflict.
Happenstance just doesn't work to resolve a conflict, and it can't be fixed by the main character (MC or protagonist) saying to himself, "Boy, that was lucky." If it was luck it had better be believable that it could happen, but I think it is weak writing to rely on luck to solve the mini-problems (sub-plots) on the road to the final resolution of the major problem introduced in the beginning.
For example, the MC can't be in a sticky situation and reach in his pocket to find a gun that wasn't [ever!] mentioned before. He can't then say, "Oh yeah, I left this in my pocket the last time I wore this overcoat." Just like in a play, you can't use props that aren't on the set when the scene opens or is carried on the stage by a character.
Even worst, absolutely worst, is to take that hand-in-the-pocket moment and go off about when he wore the coat last and why the gun was in the pocket and what he had for dinner, and, and, and...
Don't be lazy and try to fix bad writing by the use of internal dialogue. If the MC is backed into a corner, build the drama to that point so the reader is saying, "No, no don't...." Then have the MC honestly get himself out of the jam.
Like in Apollo 13, they can only solve the problem with the items at hand. Except in old westerns, the Calvary can't ride into town at the very last moment and save the day. Same goes for Superman. It is called dropping it over the transom to drop in solutions out of the blue.
A word on Superman or any other superhero. The reason the sudden rescue is allowed by the reader or viewer is because it is part of his story. He is in a difficult situation and part of the stress point is he needs to resolve it so he can go save the day.
If it was part of the other person's story, if from their point-of-view, then he does drop into the scene out of the blue. Which, admittedly, he does sometimes. As the saying goes, "Don't try this at home." Not many people get away with it.
The only legitimate fix to the need to resolve something by luck or the transom, and internal dialogue is to go back and set it up correctly in the first place. Do not try to take the easy way out of the situation with an easy fix. The readers will not buy it. They might tolerate it the first time, but do it again and you've lost them.
Write strong and brave. No shortcuts, no 'luck' solutions. Your readers deserve nothing less.