Kelsier nodded approvingly. “Consequences, Vin. You use your own weight when you Steelpush. If you’re a lot heavier than your anchor, it will fly away from you like that coin did. However, if the object is heavier than you are—or if it runs into something that is—you’ll be Pushed away. Ironpulling is similar—either you’ll be Pulled toward the object or it will be Pulled toward you. If your weights are similar, then you’ll both move.
“This is the great art of Allomancy, Vin. Knowing how much, or how little, you will move when you burn steel or iron will give you a major advantage over your opponents. You’ll find that these two are the most versatile and useful of your abilities.”