Mat's slowly getting worse, but Rand doesn't realize yet the extent of Mat's illness. It seemed obvious to me, the reader, so by extension, Rand should have realized the same conclusion I had come to. That stupid dagger was causing all the paranoia, the weakness, etc., the conclusion I came to was drawn from things Rand himself had observed. But hey - I'm just the reader. And Rand was just an inexperienced kid in a big city for the first time. Of course he's going to go off and explore.