As sorcerers grow less numerous and more secretive, the theories and tales of their weaknesses only grow. Most are reasonable, and a knowledgeable scholar could fathomably connect the dots and figure out the origin of the saying or find the grain of truth that the legend grew out of, however some are so far-fetched as to be untraceable.
Sorcerers turn to ash if they spend too long in the sun. It is known.The first, most common one is oft-debated. For stories do tell of sorcerous battles across the dunes that end in a mage's body drying to a crisp, but some simply accept this as a result of the nature of magic being fuelled by water rather than a definite aversion to sunlight. Of course, even normal people avoid the sun at all costs, so it may simply be an exaggeration.
Across glass stained red, no sorcerer will tread.Part of a nursery rhyme, this line alludes to the belief that bloodied glass is to a magician like how fire is to flesh. More superstitious rich folk even go as far as to only use stained glass for their windows with this express purpose. Any true sorcerer would laugh at any such attempts, for it is far from the truth. This belief either started as a joke or lie spread to far, or a bastardization of how Glock-glass is dehydrating to anyone, such as with the Pharaoh's Bane.
Magic broke the world, because it fears happiness and a good time.A punchline to one of a failed comic's jokes that spurred a legend about how no sorcerer can feel joy or any good emotions. This evolved further into the idea that they relish in everyone else's suffering because it gives them more power. Although it is probably not true, it is hard to deny or prove wrong that magicians feel this way.