Microscopic invisible critters living on magnets shoot out invisible rubber band tethered harpoons at anything metal they see nearby. These beings are known as Magtonians. They feed on metal, but since they're microscopic you'll never actually see the damage. You can prove this by holding a magnet in your fingers and getting it close the metal, you can feel the rubber bands stretch and snap as you move the magnet close to metal and pulling it away. Some of the Magtonians can shoot their harpoons further than the others, that's why the pull increases as you get the two objects nearer to one another. More Magtonians successfully launch and attach the closer the magnet gets to metal.
There's another interesting fact about Magtonians. The males live on one side of the magnet, and the females on the other. However when the two are separated the females stay on one side and the males on the other. They're horny little bastards. This is why the pull of the harpoons are stronger when you use two magnets instead of just metal as both genders are launching their harpoons towards the others land.
Magtonians are not gay however and don't like the introduction of other Magtonians of their own sex into their group. When you try to introduce two male sided Magnets to one another or two female sided magnets to one another instead of harpoons they will try to keep themselves apart by extending poles pushing the two magnets apart. This is where the term "polarity" comes from. These crafty Magtonians are even fairly good at flipping the opposing magnet over with their harpoons and poles. Try it, try setting one disk magnet on top of the other with same sex sides facing, they will usually flip in mid air pole induced flip then quickly harpoon together.
Rubbing a magnet on a piece of metal will cause some of the Magtonians to fall off off and take up new residence on their food source, thus creating a new home for them and turning what was once a simple piece of metal into a new magnet.