Both are real.
“They come. They fight. They destroy. They corrupt. It always ends the same.”

No, the dual personality would make the film make even less sense.
In the beginning there was nothing, and it exploded.

The duel personality theory is actually the only way the story could possibly make sense. Unfortunately, the filmmakers did a very sloppy job with the execution of any cohesive storyline. The Forest was a film of wasted potential.

I'm confident that you put more thought into this movie than the director and writers did.

if only one sister is real then who set up the tent? couldnt be Sarah since shes never been there.
if only one sister was real then why were the girls in the school scared? how Sarah didnt understand Japanese?
if only one was real then why did Michi get sad and scared at the end? if only one was real then how come they were going to keep searching the next morning???
this idea of only one sister is the most idiotic thing I have ever heard.

Jess is the one who says "she isn't with you?" to Rob.
The speculative threads on this board are more interesting than the actual movie was. Sara was kind of an insufferable witch, so whether she was an actual person or not, glad she went bye-bye.
As bad as this was, it was still better than "It Follows."

Or the husband knows what Jess was doing on her trip. Her not "being" with her means the split is gone.

Only an idiot would claim such a thing.
It was left open until the end when the boyfriend said, "Where is Sarah ? She isnt with you?"
You retards need to stop making things up.

I posted a long post about this. I don't think both were real. She was a split personality due to the trauma from seeing the murder suicide. There are tons of clues pointing to this.

Both are real. The whole thing was that Sara was going to find her sister who was lost in the forest. The forest messes with Sara's head and near the end you see Jess and shes fully alive. She feels her wrist right after Sara cuts her wrist and she runs into Rob. Sara unknowingly kills herself and becomes one of the trapped ghosts in the forest.