The reader can't know what you know
One of the most difficult things to learn when writing is to think like a reader, not like a writer.
This is one of the reasons many writers write by the seat of their pants, without structuring (or plotting) first. They write for discovery. It's so much fun to venture into the unknown and have epiphany moments when you figure things out and they just fall into place. It's addicting.
It's also dangerous.
When writing without structuring you're at the whim of chance and luck. Some days you'll strike gold, others you'll write yourself into dead-ends from which you know not how to extricate yourself. And so you re-write, and re-write again, and re-write AGAIN, desperately trying to find a solution. Again, sometimes by pure chance you'll stumble upon a solution, yet others you'll keep getting more and more frustrated until you give up and start another project.
The solution to this pain is structuring your writing first.
However, it isn't easy, and it'll require from you to know what the reader doesn't know, and then to write in such a way as if you also don't know, but of course you know everything already, and you're simply fooling the reader, and very skillfully at that.
Structuring (breaking down your story into 12 Acts, then each act into scenes, then each scene into blocks) will allow you to be the expert, yet to pretend you've no clue how the story ends. It's a lot of boring, grueling work that doesn't seem anything to do with creativity. Yet when you invest the time to do it, the actual writing is bliss. You fly through it, and you get a kick out of hiding clues, because you KNOW the reader won't get them until YOU want them to get them.
It's a new level of power, and it's scary, and dangerous, and fulfilling. Try it. You'll love it and never come back to writing by the seat of your pants (I know from experience).