That's true, humans don't like to be told that they are wrong, specially about things they care about personally. One's life is indeed personal enough to fall into dangerous territory.

At times like that the good friend is the one who just smiles, nods and makes sure they remain safe until it's over. And doesn't waste breath pointing out how they knew things were wrong or whatever once it's all over... Do they use that type of experiment often? The one in which you can't tell that you're affected yourself.