You don’t have to be mean to be a fighter. Some CEOs struggle with this (famously Steve Jobs), but Mark pulled it off gracefully. He didn’t yell at people, never threw furniture or lost his temper. He was just ruthlessly decisive, always willing to make the hard call.
So how do you low-end disrupt a high-quality, ultra-low-margin or even free product? How do you get a price lower than the $0 they’re paying today? You go negative; you actually pay people to use the product, in a currency that gets more valuable as more people join.