In the movie Inception, why didn't Arthur allow Ariadne to see his totem, which was a loaded die?
He allowed her to see it, but not touch it. The whole point of a totem is that it should act in such a way as to only be recognisable by the owner (preferably by feel).
The special weighting on his loaded dice is only known to him. When he picks it up, that instantly tells him that he's within reality, or at least within a dream of his own making.
ARTHUR: I can’t let you handle it. That’s the point. No one else can know the weight or balance of it.
ARTHUR: So when you examine your totem... You know, beyond a doubt, that you’re not in someone else’s dream.
This is also seen when Saito realises that he's inside a dream when he lands on the polyester rug.
... he NOTICES SOMETHING. And starts LAUGHING.
SAITO: I've always hated this carpet. It's stained and frayed in such distinctive ways... But very definitely made of wool. Right now I'm lying on polyester.