Have you ever been driving along with a great song on the radio and suddenly, you look around, and everyone seems to be moving to the beat? The guy in the car ahead of you bobs his head in time to your music, the windshield wipers (if it's raining) swish to the beat, random jogging man or chattering tweens in a cluster shuffle their feet like you've just walked into a musical and queued up a spontaneous choreographed dance number.
You know there's no way it's on purpose, but for that one moment, everything and everyone is in synch.
I've found that the same thing seems to happen with writing.
Remember being in High School English and the teacher would drag out whatever classic served as the week's focus? He/she would start in on the symbolism and foreshadowing and all that stuff that made your eyes glaze over because you knew someone had already written it down in the Cliff's or Spark notes, and a droning voice would fade to the background of your own mind which was screaming "they're making this up!" or "It's a shoe! A friggin' shoe! You put it on your feet and all it means is that your feet don't get cold!"
No offense to the educators out there, but the longer I work at finishing a solid WIP, the more I'm coming to realize that the little voices were probably closer to right.
Sometimes things just work. That's it. They fall into place like windshield wipers snapping to the beat of a song it can't hear. Maybe it's subliminal planning, or maybe it's coincidence, but it happens. You'll write something down and, upon editing, realize that it dovetails seamlessly with something you wrote a hundred pages earlier and forgot about.
Your MC has a skill that he's playing around with in one chapter, and come the climax, it's saving his life. Anyone who reads it after the fact is thinking you did it on purpose, but you'd forgotten when you put a throwing knife in Hero Goodguy's hand that he was playing around with a penknife to show off in front of Beautiful Damselgirl in the second chapter.
Someone drops dead, and you forgot the first time they appeared in the story they had a stomach ache... well, of course they died of appendicitis... planned it all the time... (and you'll never prove otherwise.)
The convenient need for an opening location instills your character with knowledge he needs later, but it wasn't planned that way. (Like having a kid take Karate lessons or gymnastics that give them an upper hand later, or maybe they're Quizbowl geeks who learn arcane facts that save their life in the end.)
This happened to me the other day when I was writing a scene with a background character who is the sibling of the main character. I couldn't remember his name, but I didn't want to stop and look it up because I'd loose momentum, so I gave him a placeholder name and figured I'd change it later. Then I started to like the placeholder, and decided that if the original name was so great, I wouldn't have forgotten it, so I'd just change it to the placeholder... only, when I looked it up, the placeholder WAS the original name.
It makes me wonder how many times "classic" authors did the same thing. They used a place or an object, not because it was intended to have some deeper meaning, but because it was convenient or simply the first thing they thought of. I also wonder how they'd react to all the story analysis devoted to their works.