Firefly [series] question?

So, i was watching old re-runs of Firefly and decided to watch Ariel. Then a question popped up. If Simon knows River can see danger before it comes, then why does he convince her everything is going to be okay when she refuses to enter another room or let him do something? It makes me think. Like i said, Simon knows River sees something, and yet makes her march blindly towards it. What do you think?